That's really good advice. The store has apparently lied to me in many ways. They said this fish is hardy and they are coral friendly which apparently isnt the case. I talked to a different LFS and they were willing to take it in and attempt to save it.It isn’t a certainty of course, but I’ve seen dozens of these die this way: the thinness of this fish indicates it hasn’t eaten for many weeks, possibly a month. What happens when they get that thin is that they use their livers for good energy. Once that happens, even if they do by some chance,start to feed again, the liver is too degraded for the fish to survive.
The best thing to do is have the store feed the fish while you watch. If it doesn’t eat well for them, take a pass on it.
They likely already know it isn’t eating, so they might give you some song and dance about how they only feed their fish before they open, etc. Just find a better store that will show you a fish eating before you buy it. Kind of like test driving a used car!