Owner carry backed out 30 yrs later

What is the name of your state? Oregon
My sister-in-laws father rented a trailer on property about 30 yrs ago. The owner agreed to do an owner carry on the property. Her father built a beautiful 3 bedroom home. 30 years later when he retired he wanted to sale the property. Now the original owner is claiming that he never agreed to sale the property. What rights does her father have. And how might he prove it if there was never a written contract?

your father just built someone a beautiful three-bedroom home.

[HomeGuru]

Who is on title and was there anything recorded on title in the father's name?

[nextwife]

Please tell me he didn't go ahead and build a house without recording a a properly executed and seller signed land purchase agreement/option/land contract/seller mortage or SOMETHING to establish his interest in the real estate and what terms would make it his? And that he bothered to to get a title search BEFORE entering into that agreement to establish the validity of the ownership and what else was of record against the property, INCLUDING having knowledge of any and all deed restrictions, easements and setbacks BEFORE placing improvements on the property?

[HomeGuru]

I have a mean feeling that krispen is right.