I never burn a bridge. I'll ask what's being done and maybe point out the dead. But keep it friendly and sociable. If they think meds are the only way, I might mention trying salt and high temps if they haven't tried that yet. But the way I see it, they are losing the battle already. Being boycotted by one conscientious fish keeper isn't going to make or break it. If anything, the shop could use a helping hand, not a slap in the face. Yeah, they should know what to do. But maybe they aren't educated or willing. Then it's tough. But in six months it might be a whole new crew working there, anyway. Depends on the situation, I guess.