My thinking is that if she was set up at a table, that made her a dealer, at least for the day. In that case, all bets are off and it's an arms length transaction. Both seller and buyer are expected to be knowledgeable under those circumstances. If they are not, they should not be buying or selling.

Different story if she walked in trying to sell her dead husband's gun, but it does not look like this non-deal went down that way.