Behavioral euthanasia question

I am wondering what the process is that a vet goes through when determining if BE is appropriate at all, or for a dog you are not familiar with. Example: rescue dog in foster has a history of arousal biting but no observed aggression during time in foster. Dog lunges at and bites foster from behind baby gate when foster tries to pat dog on head and wounds show two bleeding areas. Rescue decides dog is not safe to place and needs BE. Vet who is near foster wants to meet dog and assess before agreeing. Vet who works exclusively with the rescue will just take the rescues word for it and schedule BE. Is there a standard of care for this situation?