Re: The only survivor out of the litter...
If it were me? I wouldn't purchase a bully without a health certificate , certified for one year, and must be taken to your vet within 3 days of purchase. Wormed and vaccines.
Me personally, I invited the people to come see where the pups are, but before they entered the area, I had hand sanitize set up for them to use.
It's definitely your call, you should get guaranteeing that states that if the dog gets ill from genetics, a refund or another puppy is in order.
If you are already set on this puppy, I will advise you to get these paper work's I mentioned. If it doesn't feel right? maybe it isn't . and find out why the other's passed, this is your new puppy, she at least owes you that.
Life is like a box of chocolate covered