I've simplified values for discussion purposes.
I moved from overseas back to the United States where I needed a car. Before buying one, a dear friend had bought a car for his daughter in 2017 that she no longer could use (DUIs, long story). In 2018/2019 asked if I wanted to just use that car. For sure. So I drove it, and made the actual payments each month. Let's say the original car was $15,000, and since I've been driving it, I've paid about $5,000 (inclusive of interest NOT just principle). It is about to be finished for payments and we don't know what to do. It is valued about the amount that I paid but I was also paying high interest rate.
We are friends and are in no way contentious - we're both trying to be too generous rather than picky I put many miles on the car "devaluing it" I paid for a third of the car maybe, but also only used it for about half of its life He wants to say the car is now mine and sell it to me for a dollar; I want it to be his car, but I did pay a lot.
I see it as renting a house. For two years I rented a house now it is his house, he doesn't owe me anything at all. But he doesn't need the car, and it's paid off - do I buy it from him for what it's total value is, or do I subtract some from the KBB value, since I've paid $5,000 into his car? But I was also driving it.
Again, I have to stress that we are both flexible and very friendly about it - it's just the math that we can't figure out. Money isn't putting a real strain on anyone either.