The area I live in is a more rural and low-income part of MA, and for a long time almost ALL the dogs were from oops litters. People generally don't fix their dogs around here but don't really contain them either, so there are a good number of oops litters and people get these pups for free. Recently there's been an increase in rescue dogs because one shelter really started pushing their Puerto Rico dog program. So we've seen a few Puerto Rico rescues around town, along with just the usual rescues from that shelter. I don't know anyone with a pet store puppy, most will tell you they couldn't afford one. The only purebreds I see in town are Golden Retrievers, and they're the only BYB dogs I know of.
Where I work is much closer to Boston and there's a lot more money there. You see a LOT of small breed pet store dogs and most others are reputable breeders - most of these dogs are poodles, schnauzers, Bichons... what some may think of as a "foofy" dog. I see some labs and goldens around, and they all sound like BYBs but the people were convinced they were reputable breeders. Sounds like they were uneducated.