Once you get a sacrifice gift and your god cracks the altar, you should not be able to get another artifact from another altar until you are at least 2 experience levels higher than you currently are. This is intended to cut down on altar farming, but might encourage drain-for-gain (though perhaps not; it could be a bit tough without an ice box since you don’t know which sacrifice will result in a gift and staying at a low level to altar farm is dangerous).

You would still be able to get non-artifact gifts from other altars without raising your level; it’s only artifacts that would be restricted. There would be some indication either from the altar or from your god to indicate that you are too low level to get another artifact.

If the requisite experience level for the next artifact would be raised above level 30, it is instead set to 30 so it remains achievable.