My GM and CADM would have refused the same sale, as would have I. There are a few who would have made the sale, but they don't really know fish, and don't know what questions to ask. On the flip side, there are a LOT of customers who know better, but insist on doing things their way because they believe they can somehow control a fish's growth rate, instincts, etc. We ask about tank size and current stock for a reason, but some people consider this an "invasion of privacy" and get all bent out of shape over it. We are SUPPOSED TO ask certain questions to ensure our customers don't end up with dead or eaten fish, and we know that not everyone knows everything about fish, and newbie fishkeepers rarely know what questions to ask before making a purchase.
Also, I can't tell you how many people confess to buying ferrets in Nevada, where they are legal, and taking to them to family in California, where they are illegal. And then there's always the odd person who comes into the store looking for venomous snakes. (This happens at least once a month.)