I agree that dead fish in a tank does not make a bad fish store. But the store's response to you pointing it out should be taken under consideration, as well as how often it happens. Since just about all fish stores have massive amounts of water circulating through their common tank system, a decaying fish in one tank really won't throw the water parameters off that much. But from a public perception standpoint, if I owned that fish store, I wouldn't want people to see that. Anytime I've pointed out dead fish to a fish store, they've been really embarrassed and removed it on the spot.
As far as the horrible information from that one LFS, the fact that they let him walk out with 4 fish - including a tang - for a 46g tank, all at once, (yes... the LFS should've asked what size tank these were going in to, in my opinion) tells me that customer service is NOT their priority. Maybe it was just a personnel issue and not a management issue - but I doubt it.