Me and my SIL had a similar story happen to us. As we were driving down a block a dog was running loose and we got him and got him into the truck. The dog was in baaaad shape. Fleas, ticks, matted hair and his ears were burning red from infection and limping.
We bring him to our regular vet as an emergency. We told the vet we just found him bla bla bla. The vet was such a prick to us. Talking down to us like we were going to "steal" his services. Jerkoff, we bring all our animals to you and just because we said we found him, doesn't mean we are just dropping him off, we WANT him and we want to help him. F' the bill, we understand we are paying for him and it will be extensive and will pay when we pick him up. ****.
So he said he'd clean him up and he's in really bad shape yadda yadda. Later on down the road after of course we sign that we will pay for him, vet assistant calls and tells us he has a chip and the owners will be picking him up, he just got out of their yard. So we ask if they are going to press animal abuse charges on them for not taking care of their dog and letting him be in that condition. Nope and it's none of our business anymore.
We never went to that vet again. But glad the wonderful owners got to pay for upkeep of their dog.