My local petsmart is pretty good, you just have to be careful about who you let net your fish, some are good others don't have a clue what they're doing and will really stress out the fish.
I have gotten guppies at mine and had mixed experiences. If it died in the bag there was some problem and you should take it back. My first group of guppies I got there (2 males 5 females) all but two ended up dying of columnaris within two weeks. Since then whenever I buy from there I do a slow acclimation to my tank over 3+ hours, I use a little plastic betta house that is maybe 1 quart that I bought there for like $3, put the fish and pet store water in there and a couple of sprigs of naja grass for covering and throw a hand towl over the top, add 4 tablespoons of my tank water every half hour for 3 hours, let them relax.

Then I pour all of that into a big ziploc freezer bag and float it in my tank for 30 minutes to adjust the temperature. Then I net the fish out and put them in my tank. I dose Melafix for 3 days and do a 15%-20% water change on the third day. It sounds like a lot but it's really pretty easy.
I have not lost any petsmart fish since doing this, including another round of guppies and some otos.