Shops run by drow shopkeepers should always be unlit rooms.

On April 15 (tax filing day in the United States), you are charged a sales tax in shops.

Potions of booze in a liquor emporium should be automatically identified. If you observe one inside a potion shop, it should formally discover that potion.

Shops should slowly regenerate new items on empty squares within the shop, because monsters continually spawn and death drop items. Possibly, the items only regenerate when you leave and return to the level, rather than doing it while on the level.

Pets treat the entrance space to shops, or shop-owned items in the shop, as cursed, as a measure against using them to easily steal items. The latter is more likely to be effective, since the first method can be defeated without too much difficulty with a magic whistle.

Shop-owned items with positive enchantment (but not negative) have the enchantment identified, since the shopkeeper is, after all, trying to get you to buy them.

In variants with object properties, items with beneficial properties should also come identified in shops for the same reason.

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.

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.

You can occasionally find flyers in the dungeon (especially on the earlier levels) advertising shops on certain levels. Or else the mail daemon will occasionally deliver you a scroll of mail which is one of these flyers.

You can magically charge up a credit card, which when you take it into a shop makes it good for a certain amount of store credit. Alternatively, applying a credit card with charges just spits out some zorkmids and uses up a charge.

When you are inside a tended shop, that shopkeeper’s sell prices of items in your open inventory are displayed along with the item names.

Shops occasionally generate in Gehennom. They are staffed by peaceful demons, stocked with dodgy goods, and priced outrageously.

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 a new option that controls whether autopickup functions in shops. If it is on AND regular autopickup is on, items will be autopickedup in shops; if either of the two are off, they won’t.

Allow “You hear someone counting money” to show up on levels with no vault but which do have a shop.

The usage fee for reading a book in a shop is reduced to 45%, to make it so that unless you have very high Cha, it’s better to pay the usage fee than to buy and resell.

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.

You can wish for a shop type. The next shop that generates (of random type; specific shop types on special levels do not qualify) will be that type.

If you are a Monk and the game decides to generate a delicatessen, replace it with a health food store 80% of the time. This is independent from the special case for health food stores in Minetown.

Shops can sometimes generate disconnected from the rest of the level and must be teleported or dug into.

Weapons and armor that generate in shops can be randomly eroded at any erosion level. Perhaps 10% or 20% of items are eroded, the rest are not.

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).

Because general stores will buy anything, they will only buy stuff at 1/2 or 1/3 of its usual sell cost. To obtain the full cost you have to sell items at a specialized shop of their type.

Various alternate endings for the game:

• You can take over an abandoned shop, stock it with items and mimics, and settle down as a new shopkeeper, ending the game. This creates a bones file with you replaced by a shopkeeper bearing your name.
• You can eradicate the Wizard of Yendor from the game entirely and forever, becoming the next Wizard of Yendor yourself. This is done by standing in the center of the Wizard’s Tower wearing the Amulet of Yendor and invoking it. This respawns a beefed-up Wizard; defeat him and the game ends with you as the next Wizard. (It’s missing an end condition for what happens if you escape the dungeon while in this semi-powered-up state.)
• You can claim the Amulet’s power for yourself rather than giving it to a god. While anywhere on Astral, invoke the Amulet while wearing it. You get some big and unspecified surge of power from it. Furious at your betrayal, your god smites you every way they can, joined in by the other gods and the Riders, calling to bear all their priests, angels and Archons, which spawn in swarms on the high altars. (You also lose sanctuary.) You have to reach each high altar and shut it down/destroy it. Once you have done this, you win and keep the Amulet’s power for yourself, as long as you can manage to hold on to it.
• Alternatively, there is another way to do the “claim the Amulet for yourself” way: once you invoke the Amulet, a timer starts. The gods have only this much time to kill you or take the Amulet away before you become invincible to them. Would require some anti-boulderforting measures though. Or, you have to escape the Astral Plane back to the surface wiht all the gods trying to impede your progress.
• You want to break the power of the Amulet so no one gets it, and break the gods’ dominion over the world. You must invoke the Amulet while standing on each high altar to destroy it. (Not mutually exclusive with the other ending: you don’t channel the Amulet’s power into yourself, but into the high altar. In a game with both endings, you trigger the other one by invoking it anywhere except a high altar.)

Also see the Astral Escape Patch.

Closed-for-inventory shops, if you encounter them again on the ascension run, will now be open.

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.)

Fountains, sinks, and other dungeon features can generate inside shops. Using them in any way incurs a usage fee. Destroying them incurs a larger charge to be paid immediately, or the shopkeeper will get mad.

In shops, picking up an item spawns a peaceful monster that vanishes once you pay for the item properly. If you make any attempt to steal, it turns hostile. (The general principle: the more you want to steal, the harder it is to do so.)

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.

Multi-level shops, presumably with multiple shopkeepers or one shopkeeper that follows you to whichever level you’re on.

Shop generation chance increases for every level with no shop, and decreases/is reset when one is generated.