I find the notion of someone becoming responsible for someone else's "sin" by allowing them to purchase goods from your store to be both hypocritical and completely devoid of theological backing.
I will say I've heard the proprietor of a gun store relate a tale of a guy coming in to buy a gun. "Why do you want it?" he asked. "To kill that <n-word>," he replied. The potential customer further went on to say that if he did
not sell him a suitable weapon during his visit, that he would sue him for racial discrimination (the patron was black, the owner was white). In the end, he sold the man a 12ga double-barreled shotgun, figuring that if he was going to be railroaded (blackmailed, really) into this situation, he did not want the guy who was going to be on the receiving end of the blast to have any chance of suing
him (the business owner) as an accessory. The story (which may or may not be apocryphal) went that the customer waited until the victim showed up, emptied both barrels simultaneously through a screen door (killing the victim, obviously) and the recoil was enough to temporarily injure the (inexperienced) customer such that it aided in his apprehension. I do not know the ultimate outcome, but it was an interesting conundrum. I wonder at exactly what proportion of responsibility the owner should bear, compared to what proportion he
believes he bears.
--Patrick