Amy Barnes, who placed the ad, does not appear to be an accredited breeder with the Kennel Club. But you said the litter was an accident, so she may not have intended to breed, but was irresponsible.
It is good that she will let you return the pup if necessary - see if you can get a signed contract,even if you have to draw it up yourself.
Sounds like you went to the home to see the puppy, that is good, so you can see what kind of home puppy is from.
For some reason when I click on the ad, it takes me to the right page, then tries to switch to an unavailable MySpace page
