Good breeders pick puppies out for you rather than allowing a buyer to choose their own pup. There's a good reason for this. The breeder should be concerned with matching a pup with your home and family and who knows the pups better than the breeder. Ask other Border Collie owners about the breeder, as well as rescuers and anyone else associated with the breed. If they are unknown in Border Collie circles, it may be for good reason.
Good breeders have good reputations.
Rescuers are also a wonderful resource as we know which breeders' dogs are ending up in rescue. They might be a puppymill, producing an overabundance of dogs. Or the pups they produce might be ill-tempered. Whatever the reason, dogs from their lines ending up in rescue is a bad sign. This can be a little misleading, though, as some disreputable breeders still offer guarantees, knowing full well that you're unlikely to return a dog after you've become attached to it emotionally or sue them over several hundred dollars.