Anonymous wrote:OP this is lovely of you. Do you have the son's contact info if the neighbor asks to see the dog for a visit later?
Most rescue dogs are supposed to be sent back to their rescue organization, if the person who adopted them is unable to take care of them. At age 12-14 I wouldn't worry about this too much.
I would call the dog's vet (or ask the son to call them) to set up a check-up visit, especially if you have a different vet, and want to transfer the dog to your vet later on.
Properly rehoming a dog to a good home is taking care of them. No rescue would argue about this.
+1 to asking current owner (or their caregiver) to authorize release of records from the dog's last vet, and +1 to taking the dog to your vet for a preliminary check-in visit for baseline info, any vax that may be overdue, and a parasite screening. Consider quarantining the new dog until you know it's not carrying anything you don't want your dogs to share, especially since you regularly found it outside unattended. You'll also need to transfer its license or file for a new one.