Pet shops – unethical, to what extent??

Hello, I just wanted to ask a few things about pet shops. I haven't been in Japan very long, and I've been told about the heartbreaking cycle of pet shops when the puppies don't sell.

I guess I wanna ask is it ALL pet shops??? How long do the puppies have to be sold?? Do they often sell a lot of the puppies in time?? Where do these stores get so many different puppies from at high frequencies?? Is it 100% all pet shops WILL euthanise puppies if they're not sold and move on like nothing happened???? Do they employees themselves not care about the animals???

I guess I just don't want to believe it but I saw a pet shop earlier today and got lost in the cuteness then remember on my way home. Any insight would be appreciated.

by mimi_stk