The subplot with Walter's dad

As implied by the common owner of both houses, maybe they intended to make a sequel, where the dad had the same problems with the house. The owner probably wanted to get rid of those old houses. Also maybe the son paid him a visit and then was when the problems started, implying that the son always brought bad luck with him...
Just some thoughts.

Justice. The dad screwed Walter, a nice guy who didn't deserve it. The final scene gives us one last bit of joy - Walter's dad is going to go through the same trial by fire. We doubt HIS relationship will endure.

The *main* reason for Walter's dad's subplot is to show that Walter was a good guy. Even though it wasn't his debt, Walter repaid the bands for the money his father stole from them. The end cap scene just shows that his father gets his comeuppance by getting reamed by the same old lady that reamed his son (although Walter's house after restoration was now worth more well more than he paid for it and the restoration - and it was beautiful to boot).

I came here to ask this very same question. So obviously the old lady and “Carlos” are running a scam on many people. But is it just sheer coincidence that they scam both Tom hanks and his father?

Back then in the mid late 1980s when i was a kid, i thought Money Pit was funny because Tom Hanks was in it along with Shelly Long.

then these days i find out some in jokes etc about scammers etc and how sketchy some house fixer upper people are