Once upon a time I had a car, a daily driver. I kept it clean, vacuum/wash/polish with crazy waxes and the works. Stressed out about people riding with dirty shoes, drinks, etc., and when I asked myself why, the usual self-justification was "ah it's for the resale value." Hearing relatives get charged various fees at lease returns just fed that attitude, even though I owned the car outright. One day it was time to replace the car, so I brought it to the dealer as tradein. They scanned the VIN, looked in their computer, and just quoted me a price without ever looking at the car, either cosmetics or mechanicals. That was the day I decided that I own the cars, not the other way around, and this attitude slowly expanded to real estate too ;). So now there is a clover field in our front yard and I ripped out the irrigation too. When we eventually sell this home in 2060 the buyers can take it or leave it
Of course, you should never sell the car to the dealer and should always make the effort to sell private party, which will often get you 50% or more greater than the dealers best offer.