Just to add, anecdotally, most pets from a pet store will likely be fine, but it's a bit like saying "I ate unpasteurised cheese all through my pregnancy and baby is fine." or "I drive without a seatbelt and nothing's ever happened to me." The way pet shops breed and treat their animals is not fine, at the very least the animals do not get the attention that they need.
DP and I rehomed two rats earlier this year who had originally come from a pet shop. Two girls, utterly gorgeous. They came to us in their cage that the family had been advised to buy. The cage was quite small by rat standards, bar spacing of about two centimetres, two shelves, a metal rung wheel and a few of those hamster nibble things that clip onto the side of the cage.
Even the slightest bit of research online will tell you that it was wholly unsuitable, but you trust what the pet shop tells you about what you need. We couldn't afford a new cage for a couple of weeks but we did make sure that the environment in it was more suited. However the girls could have gotten out of that cage at any point had they wanted too. In fact one of them sat with her head poked completely through the bars as if to prove a point.
That's completely ignoring the fact that the same one was so terrified of us when we got them, that it took her a week to even come out of her little house when we were in the room, and we sat in there for hours upon hours just talking at her. Part of that would have been her early upbringing.
I've gone into shops and when asked "Can I help you?" I've asked questions about products and cages and so on and so forth, just to see what answers I get. Very rarely has a staff member recommended a suitable cage (usually hamster cages or smallish temporary rabbit cages with large bar spacing get suggested), they don't even know what hammocks are or if they do, they say that they have ferret ones but why would we want them for rats? I've even had one staff member tell me that a rat would be perfectly happy with a bare cage so not to waste money on lots of toys.
It is hit and miss, but I'd rather not give money to a chain who is hit and miss. Though the welfare of the animals is the worst bit. Rodents especially come from rodent farms, which are really upsetting. A pets corner local to me in Sussex get their rats and hamsters from a rodent farm in North Essex. Those animals are bred in tiny plastic containers, then driven down 2.5/3 hours minimum (or more when traffic is bad) in small cages and boxes as they deliver 5 or 6 rats/mice/hamsters/etc to various stores in the area to be deposited into glass sided boxes which does nothing good for their respiratory systems what-so-ever.