When he picked up the gun and said "Wow only $1600", what would be wrong about saying "Yeah, its a great price. I would have bought it if it wasn't a salt gun." If he asks what that means, explain it. Don't tell him its garbage. Just let him make a more informed decision. It might be his dream gun and a discounted one is all he could afford, in which case he would still buy it. Personally, if he wanted to talk about it I would ask a question of the dealer to bring him into the conversation about the condition of the gun. Keep it friendly. The dealer would no doubt point out the low price and why he thought that was fair. If the dealer got angry that I discussed guns with a customer he's not someone I want to deal with anyway. I hope if the situation was reversed someone more knowledgable (and there are plenty) might do the same for me.
