Hopefully I'm going to go to the bad lfs at the weekend and mention a few things to them... like the poor DP ( I think) covered in whitespot with only half a tail, and bettas they have in that are nipped etc, maybe the crappy size of their 'goldfish' tank (seroiusly, its between half a gallon and one gallon... and last time they had 1/2 gallon tanks with about 3 tetras in). I'd say the best method is to tell them straight. I'll probably go with 'What fish is that' with the DP (its not labelled), then say how it doesn't look very healthy. And if I can manifest (hey, I don't know what that means, its a good word though) myself as an intelligent, fish loving 13 year old, I might even be able to wangle myself a mental note that I would make a good employee .
Sorry, I was rambling on far too much and have nicked the thread. As said though, if you don't say anything, what will happen? The fish will die, to be replaced with the same or something even worse.