Never been to a Petco, but I work at a Pet Pupplies Plus, and take pride in what I do. I have convinced my boss to order our BPs from a good friend of mine who just needs to get rid of his normals, so I can guarantee that the snakes we get our 100% healthy. Because some snakes we have received from "large" reptile distributors have had RI.
I take pride in what I do because I feel like I have extensive reptile knowledge, and if I am stumped on a question a customer has about a reptile, I instantly come to this website, or other credible ones to educate myself.
I do laugh at some main chain pet store employees that tell me that feeding my baby ball pythons every 5 days is "power feeding"

So I recommend that what people hear from pet stores they take with a grain of salt, and do research for themselves. After all, before I fell in love with this site, I looked a tons of different websites for snake information.