There should be shops that generate in Gehennom; they have amazing items, but only take payment in gems, with better gems buying better items. There are a couple issues to resolve, though: first, the shopkeeper has to be buffed enough that you can’t just kill them; and second, by Gehennom most randomly generatable items aren’t super useful to the average player.

One way to address the first issue could have these not appear as a traditional shop, but as some sort of wandering peaceful demon species (or randomly peaceful members of existing demon species), each of who offers a single item in exchange for a set list of gems. When paid, they summon the item out of a globe of darkness, so they can’t be killed to get it for free. If you decline the offer, they will turn hostile.

The second issue could be addressed by any of the following methods:

• Sell a limited set of items known to be useful in the endgame such as full healing and gain level potions, genocide scrolls, magic markers, etc.
• Sell items that are highly unlikely to be generated other than via a wish, such as figurines of high-level monsters.
• Create entirely new powerful items, which can only be purchased from those shops and cannot be wished for.

Archeologists never get charged an unidentified markup in shops, because they know when a shopkeeper is trying to cheat and take advantage of their lack of knowledge.

Replace the random markup on only some unidentified items sold by a shop with a multiplier that is always between 1.0 and 2.0, but is always the same within the same shop, and is applied to all unidentified items in it. The multiplier is biased towards the lower end of that range by taking the square root of a random number from 1 to 4 (or mathematically equivalent constructions that minimize reliance on floating point calculations in the code, such as taking the square root of a number from 25 to 100 then dividing the result by 5).

You should be able to give a potion of see invisible to a shopkeeper while you are invisible. They will then quaff it, and stop blocking their shop door. Depending on implementation, if the shopkeeper’s see invisible is temporary and later times out, once they can no longer see you, they will again block the door.

When you identify a piece of worthless glass that belongs to a shopkeeper, they get angry and attack you because you have exposed their fraudulent business practice.

A shopkeeper who hates you (e.g. for having stolen from them) will be reluctant to serve you and will insist you wear a shirt and shoes before you enter.

In variants with racial shopkeepers, the shopkeeper can also hate you on principle without you doing anything wrong. In variants with Convicts, their striped shirt could be unacceptable for purposes of having a shirt.

Shopkeepers value empty wands at 0 and will not buy them.

For every mimic you personally kill inside a shop, the shopkeeper gives you a token fee of 5 gold (or store credit) if you talk to him afterwards.

If you clear the shop of all mimics (with some minimum amount of mimics required), the shopkeeper could give you a free item of your choice.

You can pay a shopkeeper a small fee to go take an item from the floor of his shop and deliver it to you, so that you avoid running into mimics getting it yourself.

Keep a counter on each shopkeeper representing the number of times a pet has picked up a shop-owned item in their shop (or a shop-owned item inside containers they are carrying). Every time this increments, use it as an increasing chance that the shopkeeper will become aggressive towards pets picking up their wares, with messages like “Kabalebo shouts “Hey! Drop that!” at Fluffy. Fluffy drops [item].” Once they are past that point, you can’t use pets to take their items anymore.

The point on the counter at which the shopkeeper stops playing nice should be roughly some fraction of the area of the shop, to strike a balance between large shopkeepers being more lenient and not allowing you to clean out all the tiny shops in Minetown. A rumor could be added for this: “They say that mom-and-pop stores have lower tolerance for thieves.”

Unspecified whether the counter should increment when a non-pet picks up an item in the shop. Probably not, since this is a fairly rare case.

Make shopkeepers more susceptible to being paralyzed or put to sleep than they currently are, so it is easier to directly but non-lethally steal from them.

After a pet removes a shop-owned item from a shop 5 times, the shopkeeper stops permitting pets in the shop.

Items generated in or sold to shops are marked as being property of that shop, and when you buy it properly, this marking is cleared. When you attempt to sell an item to a shop that is currently marked as the shop’s property (meaning it was not properly paid for), the shopkeeper just confiscates it without paying. This prevents you from directly or indirectly stealing the same item over and over again and getting paid for it every time.

Whenever you use a shop-owned item to make a wish, the shopkeeper treats the wished-for item as theirs, in addition to the usage fee.

Shopkeepers remember when you have robbed their shop even after you pacify them, including in a bones file with a player of the same name who had robbed the shop. They treat former robbers as suspect, and enforce stricter rules on them and/or raise prices for them.

To reduce the reliance on general stores and the tedium of throwing scrolls into shops to price-identify them, all shopkeepers will buy scrolls of identify, or at least look at them and go “ew that is a really cheap scroll” so you can figure out what the identify scroll looks like.

Some monsters, when dealing what otherwise would have been a killing blow, instead leave you at 1 HP, strip you of some or all of your possessions, and possibly vanish/teleport. Shopkeepers in particular may decide to do this (but some may still decide to kill you).

Dwarvish shopkeepers never ask you to leave your pick-axe outside if you are also a dwarf, because they understand the deep cultural offensiveness of asking a dwarf to set aside their pick.

If you directly steal from a shop, even if you pacify the shopkeeper afterwards, the word goes out and other shopkeepers may then charge you higher markups. (Even if you killed the shopkeeper, but not if you killed them without actually stealing anything - perhaps the Kops are sharing this information around).

Expand the behavior of the ‘unpaid’ object flag so that it tracks items that you have stolen from shops or looted from shops with the shopkeeper absent or had a pet steal. Unpaid items outside their shop can render as “stolen” in the object name, and attempting to sell them inside a shop (even if not the same one it was stolen from) will just cause the shopkeeper to claim it and give you no money.

Add another variable to the eshk shopkeeper struct, which tracks how much they dislike you. If you break their door or rob them, they’ll continue to dislike you even after you compensate them. A shopkeeper who dislikes you strongly will inflate their prices. It may be possible to get them to stop disliking you by buying lots of things from them, but probably not.

If you try to sell a zombie corpse to a shopkeeper, they get angry. Or maybe they merely won’t let you into the shop if you’re carrying a zombie corpse, the same way it works with digging tools.

Gently nerf the ability of pets to steal from shops, so that a player with a stack of meatballs or a magic whistle can’t clear out an entire shop. Suggested ideas:

• Make apport less easily exploitable, requiring more in-depth training than just feeding your pet after it drops items next to you.
• Track the total amount of value lost to a shop by a pet moving items out of it. Once this value exceeds some threshold, the shopkeeper intervenes, either by turning hostile if you continue letting your pet steal after a warning, or attacking the pet.
• Track items that have been stolen from a shop (probably by marking them with the monster ID of the shopkeeper). You can’t resell stolen items; the shopkeeper won’t offer any money for them, instead they will grin and say “Thank you for returning my stolen [item]”, taking ownership of the item. However, this doesn’t solve the problem where you really do want most of the shop’s inventory for yourself.

If possible, work in a “pet-ty theft” YAFM somehow.

When you kick a door that is closed but not locked, it can just crash open and become an open door instead of breaking. This is only if you kick it in one specific direction, deterministic based on its coordinates. Diagonal kicks can count as kicking in that specific direction, but kicking perpendicular or opposite will result in the door breaking like usual. If you kick open a shop door like this and don’t destroy it, the shopkeeper yells at you a bit but doesn’t demand money.

The cost of breaking a shop door is at least partially non-deterministic, so you can’t figure out the exact amount the shopkeeper will demand in advance.

The “You hear someone cursing shoplifters” message replaces “someone” with the name of a known alive shopkeeper on the level.

Wearing a cheap plastic imitation of the Amulet of Yendor gives you the sucker markup in shops.

Shopkeepers will buy identified glass for the same few zorkmids they will buy it unidentified, rather than refusing to buy it, because it makes no sense that they buy it when the player doesn’t know that it’s glass and refuse to when the player does.

Shopkeepers won’t buy wands from you if they are empty.

When a monster picks up an item owned by a shop, its base price is deducted from any gold they’re carrying and gets transferred to the shopkeeper. If they’re short on cash, they don’t have to make up the difference at all.

If you try to buy a high level spellbook in a shop while outwardly looking unqualified (low XL, low Int, Barbarian), the shopkeeper raises an eyebrow and condescendingly asks you if you’re sure you can read it. This can help you informally identify high level spellbooks.

Shopkeepers can be cancelled. When cancelled, they won’t buy or sell any items. They will still react to theft, but they can’t be paid and they don’t offer any money or claim ownership of items you drop in their shop.

Shopkeepers charge a hefty fee for digging pits in their floor, hundreds or thousands of zorkmids. The shopkeeper will warn you when you start digging.

Itinerant merchants who, if chatted with, offer one of several non-renewable trades. Generate on stairs, path to the opposite stairs, and once they reach them they disappear forever from the game. Generated with the requisite inventory to make all their trades. Always peaceful. Tougher than shopkeepers, since they have to defend themselves out in the dungeon. If you kill one, no more will ever spawn.

Chatting with a shopkeeper makes them offer to appraise your inventory; if you accept, they will automatically type-name all your unidentified and un-type-named items (that they would be willing to buy) with the price they would buy it for.

Shopkeepers should pay you a small fee for killing a mimic that was generated in their shop. (Or at least give you the corpse for free).

Assuming that shopkeeper identification services have been implemented: Shopkeepers of stores besides general stores will identify any item that can be sold by their shop for a fixed price. General store shopkeepers either don’t identify anything, or can identify everything for you with an exponentially increasing price.

Something would have to be done to avoid trivial item identification of items that shopkeepers sell only one or two of in a class (e.g. showing a bunch of potions to a delicatessen shopkeeper, they reject most of the potions as ones they wouldn’t sell, and informally identifying the potion of fruit juice by not rejecting it). Perhaps they should only offer identification for items for which they sell the entire object class.

A levelable haggling skill that gets you better prices in shops.

Shopkeepers can summon a minion or clone to guard any second door into their shop if one should happen to exist.

You can douse an angry shopkeeper in Lethe water to make him forget you.

Shopkeepers track your petty thefts, and automatically anger if you steal a valuable single item or 50% of their stock or items totaling more than 1000 zorkmids.

Shopkeepers recognize items that they originally owned but were stolen from them by pets, etc. They reclaim ownership of those items if you return to the shop with them, or possibly get angry.

If you use any stolen shop items while in the shop, the shopkeeper recognizes them and gets angry at you.

You can haggle with shopkeepers to sell items. They’ll make an initial lowball offer, you can counter with something, they can counter it, eventually converging to a mutually agreed price. Sometimes refusing to go lower can convince the shopkeeper to accept the higher price; sometimes the shopkeeper will refuse to go higher. If you make an offer lower than their current offer, give them a YAFM ‘[shk] raises his/her eyebrow. “Deal.”’

Usage fees can never exceed the original cost of an item, and when you buy the item, any usage fee is removed (it’s only charged if you use the item without buying).

If you are completely armorless, shopkeepers will block their door and prevent you from entering.

Shopkeepers gradually over time replenish their in-inventory gold, but only if Ludios is not yet generated. Any gold that is replenished to shopkeepers is removed from Ludios’ large vault when it generates.

Shopkeepers refuse to deal with invisible customers completely.

A way to allow the player out of locked shops they teleport into. Possibly chatting to the shopkeeper, or trying and failing to open the locked door from inside the shop.

Sell price depends on Charisma, whereas buy price does not. (Slightly more flavorful.)

Shopkeepers type-identify any item they sell you. (This allows the player to type-identify an item by selling it and buying it back.)

You are not asked “Pay whom?” if you are standing inside a shop, it just selects the shopkeeper whose shop you’re in. Also, you are not asked if you can see multiple shopkeepers, but don’t owe money to more than one.

Racial shopkeepers give the player discounts. This could be in the form of a direct buy price reduction (must be capped at 50% of the base cost though to prevent farming) or treating the player as if they had higher Charisma. If the shopkeeper hates your race (for example, elves versus orcs), they will also block the entrance to the store as if you were carrying a pickaxe.

Shopkeepers should be aware of when you use your pet to steal from their shop, and they should raise their prices to compensate, eventually not letting you reenter the shop. Alternatively, the shopkeeper should simply block the entrance as long as any monster in the shop is carrying unpaid items, but this could be circumvented with a magic whistle.