Maybe make him watch one of those flipper shows where they show the amounts up on the screen and the flipper is racing to get stuff done so that don't have to make more mortgage payments--every month that goes by and you are carrying that house--that is where their business succeeds or fails. That carrying cost is very, very real, and can sink you if you don't get on top of it. I think that is why Dave Ramsey is always telling everyone to sell their rental property to get out of debt. . .
I am sorry this deal fell through, it must be so frustrating.