Ohhh I had an experience with something like that not to long ago with a LpS that is near me. It is too bad too because they are soooo close to me and the LFS that I love is 1/2 hour drive.
I went to this place for the first time actually a few months ago and saw cruddy tanks and such and their plants were basically rotting. Anyhow I went back a few weeks ago thinking I should just check em out again maybe they were having a bad week. NOPE their stuff was NASTY. I had my kids so they looked while I was like

and the gal comes over and says...Ya need some fish HUN??? Now here comes my girl power b**chatude commin on. I hate being called HUN by complete strangers, so very rude. LOL Anyhoooo, I told her no thanks I see you have a few issues with your tanks and wouldn't want to infect mine. SOOO she said OH? Our tanks are fine. So I got on my soap box and told her to follow me...we stopped at tank #1...3 dead fish rotting, (mid afternoon while I was there so they had plenty of time to get em out when they opened) Same issue in tanks all on that wall...ATLEAST 1 fish dead and rotting on the bottom. The next wall of tanks were a bit better with the no dead fish thing but one tank in particular had 3 cool looking green spotted puffers. one looked like to be a baby of the other 2. ANYHOOO they allllllll had some type of fungus on them, one had a full fungus cover on its eye. I showed her that and she told me they were fine, it was just muck and would be cleared when you took it out and put it in the bag to bring home.

I about freaked but held back and said to her quietly are you friggen kiddin me. Those are sick!!! fish you should be treating them and Q'ing all your tanks!
My LFS I go to is amazing, their tanks are far from spotless but they have wonderful quality fish. A little more pricey but I would pay for the pricey over the dead in a week variety any day!!!
I wish LFS would get in trouble like puppy mills and people who make dogs and cats suffer!!!
Hugs