To add to the "puppy farm"/backyard breeder comments.
My friend got a pup at the start of lockdown. Yes, I know. It was an "accidental mating" resulting in a crossbreed. Cute pups, £300.
Funnily enough, the same "accident" happened again and the dogs had another litter in October. The cross breeds are being sold this time with a designer name (like maltipoo, but this is a bloody weird mix of dog so I won't name) for nearly £2000. Brilliant, so back to back breeding of dogs and all the health implications there, ridiculous prices, etc. No vaccinations done, no chips, no health tests done, pups won't have seen a vet.
My warning would be that someone disreputable will always tell you what you want to hear. So you may be told "last litter" because that sounds responsible and puts the pressure on to buy. But that's no guarantee, is it?
A good breeder with a planned litter will have a waiting list. It's worth it in the long run to research breeders, research a breed and join a waiting list. A reputable breeder will want to interview you properly.
FWIW, I have fallen prey to this too. I thought I'd found a great breeder years ago when I was a lot more naive. KC registered etc. They let us all take pups home at 6 weeks as it "let them settle before Christmas" (pups would have been 8 weeks on 21st December). Breeder said it would be fine. I knew no different and as they'd seemed really knowledgable until then I went with it. Ended up with a dog with horrific separation anxiety and some low level behavioural issues. I was experienced with older dogs, but I'd never had a puppy before.