I recently sold a house and when the people were trying for a loan, I believe that in order for the specific loan they were trying for to go through, this, and this and this had to be done....but I don't believe they said the the buyer had to do it, just that it had to be done or the money put aside to do it (in that case by the buyer) for the loan to go through. This was my step fathers home and was a fixer upper that they got at $20K less than appraised value. As it turned out, they didn't go with that loan company.
I agree, your son should be careful, what if he fixed it then the sale fell through...