Not to be funny NQK, I always worm any new dog on the yard. I have gotten dogs from people who claim to worm their dogs on a regular basis but the dog still has worms. Also give the dog a high-protein feed (not so high as to cause kidney failure). Take him to the vet immediately or you might come home to a tragedy. The owner may blame you for the loss. This is just my opinion but do what you can and if that don't work, take him back.