Never sell cars to friends and family.. that for sure is a nightmare.

You want to know the hitch.. here it is. Someone brings you a car to look at.. Example Expedition with 170k miles.. check engine light on.. You check codes, fix a vacuum leak.. charge minor labor.. customer leaves. A week latter they call and now it has a miss.. it needs a tune-up.. they pay for tuneup.. oil change.. they leave. Week latter now has a vibration.. and they have "Spent money" getting the car fixed. Now they have spent money with you.. had the car to your shop on multiple times.. keep having problems and want you to do something about it. Once you layed hands on it and performed some serious a "ring on the finger scenario" happens.

Point is.. sell a car... big as-is on the paper work. Tell them to bring their mechanic to inspect it.. he can fix it when something goes wrong. I never tell people I fixed this and that on the car, cause if you do.. they will assumme you will fix it when it breaks cause you missed doing so when they had bought the car.

The more miles and years on a car.. the bigger the headache.