My primary concern is that the dog has a great upbringing and life and whilst it will suck for me or the old owner, that's fine as long as the dog is looked after. The guy did properly feed him, and wasn't malnourished so I am happy with that.
My approach tonight is going to be as follows:
(1) Verify that the dog was his. Photos / vet bill etc will suffice (he has pretty distinctive markings). [Magic's suggestion re: proper record of vaccinations is key, thanks!]
(2) Ask him for his story of what happened.
(3) Ask him why the dog was not tagged or chipped.
(4) Ask him what he did during those seven weeks to find him.
(5) Ask him if he is attached to the dog.
If any of the responses to the above are negetive, I am keeping him. Once he has passed this stage, I will explain what I did to find him, to home him and the costs involved.
He can choose whether to pay me for the costs (R600 for vet costs, R200 for food/lodging, R100 for collar and R800 for his bed/bowl) or we can call it even and I keep the dog. Hell I might even chuck in R500 his way to keep him.
The choice will be his.
However, last test will be if the dog responds to his call. No response, sorry for you the dog has moved on.