“What’s all this?” Seregil whispered as the bowyer went to adjust the wands.
“I’ve heard it said that he won’t sell a Black to anyone who can’t hit all three targets,” Alec whispered back, strapping a leather guard to his left forearm.
-Luck in the Shadows by Lynn Flewellin
This is not a bad idea for marrying two seemingly incompatible goals: making magic items feel special while providing a convenient way for the players to buy them.
Let’s say Bann the Bowyer makes the best bows. He sells +1 (Bann’s Blacks), +2 (Bann’s Special Blacks), and +3 (Bann’s Special Reserve) bows. To earn the right to buy one of the bows, you need to hit a difficult AC on 3 out of 4 shots with your basic attack. The AC for buying each class of bow is 20, 25, and 30 respectively. (When you’re making your shots, you get to use the bow you’re interested in.)
Bann works in a small village, so he doesn’t have much protection against robbers beyond the archery skill of him and his apprentices; but he can inflict Bann’s Curse on thieves: “Every time you draw arrow it will hunger for your friend’s heart.” (A natural 1 with any bow attack auto-hits an ally. The curse ends when you return Bann his stolen property.) “My bows have been stolen before,” says Bann, “but they have a way of coming back to me.”