This is what the rescue I got Samson from says about themselves
-- We are a 501(3)c nonprofit organization approved for rescue in Alabama and Georgia. We are run entirely by volunteers dedicated to the rescue of unwanted, neglected, and abandoned boxers. We are always in need of qualified homes for life for our dogs, transportation, temporary foster care, monetary donations for veterinary care, high-quality dog food and other supplies.
Boxers come to us from shelters, as strays, and owner surrenders because of death, divorce, or relocation. They are housed by foster homes where they are temperament tested and seen by a veterinarian for shots, heartworm testing, and spay or neuter. ---
If i remember correctly you want to make sure they do state they are non-profit and like Barb said, also a member of ABR. There's a boxer rescue link on the front page, all of the rescues listed are approved and I would have no problem donating to any of them...