✔ 最佳答案
Well... A pure bred dog is not only a dog of only a single breed but also a dog that was bred for purpose through selective breeding. It's also a dog that is bred to breed standard.
Since you're getting this dog from "unknown source" the dog is not a genuine pure bred even if it is only Labrador.
You won't be able to tell and there's no test you can do. If the dog has webbed feet and an otter tail and looks like most labs then it's a lab... Even if it's not "pure bred"
Why are you buying a dog from an "unknown source" If you're buying it don't you know who you're buying from?
And by the way I have nothing against mixed breed dogs. I have a lab mongrel and he's a great dog. I do however disagree with buying dogs from people who breed indiscriminately.