Make sure she shares her dog's whole medical history with you. Since you are in the same town, find out the name of her vet and have your vet get her records from hers. That way your vet and you can review those records so you can get an idea of what you may have to deal with. That should help ease your mind a bit. Also, ask her if she'll take the dog back if it's not working with the dog you already have and take her on a trial basis until your questions are resolved. Good luck.