I don't buy fish from petco, just petsmart. All fish I've ever gotten from petco had the dreaded worms. Sometimes petsmart fish are sick, but that's nothing a bit of care or meds can't fix. I spend a lot of time watching the fish and if they aren't good enough, I leave them and come back days, weeks later to see if any are better.
Anything that is living has the possibilities of just dropping dead and that is quite a common thing depending on the animal. My tanks have been up and running for a long time, darn near perfect all the time and I use well water, so there is no chemicals at all. I've bought from breeders before and have fish die from...who knows what. Even with the best acclimation, time and care, they can die and being on the poorer side, adding fish cost, shipping cost and then for them to possibly die is never going to be a small enough risk to take. If I was rich and buying online fish and not caring about a few deaths, I'd think myself reckless with money.
Any and all local small pet stores just suck, crappy fish, too pricey, not enough to choose from, tanks are just muck[algae on every freaking thing] and too far for me to be picky and come back.
Anyway, I don't need a bottom fish. If I manage to find a local member one day with a good deal and a great fish I just gotta have, I may just go for it.
I heard some have worked out with a rainbow shark, so I will try that since my fish are fairly calm and the tank will have tons of holes and hide outs as well as a section of just wood. He doesn't do much but watch his den anyway. Most of the time I cannot even see him.