Petco here in Orlando is cheap, but horrible. One day I went in there to kill some time while waiting for a friend.... and there was a dead goldie in every one of the 6 goldie tanks ;p That's not counting the tons of dead ones in the feeder tanks.
Petsmart is much better, but even they have bad weeks...
Just spend some time looking at all the tanks... look for dead, sick, or lethargic fish. They're pretty easy to spot, even for us newbies.

FTB