How does he know who paid him back or not considering he used a common address for everyone.  What if someone sent it in pieces or returned only 90%, he can't just go by the amount received.

Is this going to be a best guess scenario where people will end up having to prove they sent it?

I wish he would just start paying out with the btc he has received back, there is no reason to hold on to them.  Manually would be best since he seems to have some problems with scripts.