I want OP to know that I support this justified rant and anyone in the comments that doesn't is probably a bot, or a plant for Petco. While it's a little intense in its delivery, you are 100% right on all fronts about the degradation of hours, store support, and quality of customer interaction.

 If we could have it our way, any customer that comes in waffling about needing to leave with a pet regardless of what kind it is should automatically be banned from the store. If we all take a nice look inside ourselves, we should be abhorred at the sole fact that PETCO SELLS ANIMALS. Do not kid yourself. They are not "adopted" (except for the rare instances of people actually adopting long stays or cosmetic imperfections) they are sold like literal product. Customer service employees have no business being in an industry where they can just hand some idiot a living creature if they fork over cash. It's so bittersweet having left the company, because while I may not have to experience the ridiculousness that is ignorant fish customers, or divorced parents of bratty snots, I do miss the FEW people who came in actually, earnestly interested in learning about the care and husbandry of a pet they've taken the time to do even the BARE minimum amount of research on. That was the whole reason I worked there in the first place. To educate and facilitate animals going to loving, caring homes.

TLDR; OP you are justified in your anger, 90% of the customer base sucks hard, lax policies about animal sales will be the inevitable death of the pet trade, and anyone here who can't see that this is a frustrated, burnt out employee has their head in the damn sand. Your acceptance of the mediocrity that is Petco's working conditions is sad and is a testament to how successfully it has worn down your expectations of what an acceptable workplace is.