If I were Petco I wouldn't focus in having animals in stock but more behave like a store that sells kitchens or w/e...
Just have a few show models that look really good in awesome enclosures then make deals with suppliers (breeders) to stock animals on request.
You can show someone interested the catalog of what's available with pictures and basic husbandry needs (like enclosure sizes).
If someone then wants an animal you can send em home with a booklet on their chosen animal (Caresheet) and tell em to come back in a week or so when you'll have it ready.
Customer has more time to prepare his setup (bought at your store), your store and reputation look better, you sell a better product and your customers are happier.
Damn I should be CEO at Petco.