Petco goes through suppliers like a flu victim goes through kleenex.

They will use someone for a while then go elsewhere for a better price or because you irritated someone.

They also irritate some of their suppliers by not paying for animals that are replaced by petco then charged back to the supplier on a subsequent shipment.

I used to work for one of their tank and animal suppliers so I know this first hand. Though it was a few years ago I doubt it has changed.