There's a lot of reasons to dislike Petco... Amazon is able to ship a dog crate to my door for almost 3x cheaper than Petco sells them in stores... but hiring part time employees to clean cages should not be one of them. I've visited a lot of local pet shops in a lot of different areas and I've never met a single non-managerial employee that was full-time with benefits. And most of the managers were blood family to the owner. Employees at local shops are often part-time kids too. Some of these were exponentially better than Petco and others made chain stores look like animal heaven.
It costs a lot of money to pay full time wages with benefits for a job. If a position only brings the company in X dollars and full-time wages plus benefits cost X +Y, either the company eliminates that position or goes bankrupt and the position is lost anyway... or they raise prices and lose their customer base. Pet shops go out of business all of the time... it's a tough business to run. I can't imagine the average Petco makes much profit off of their live reptile sales... probably enough to cover some overhead and juice the sale of more profitable equipment.