I generally would buy a used vehicle from a private owner, mostly an older couple or a person past 60 years of age. Reason is: 1. They generally change the engine oil and other vehicle maintenance as scheduled including tire changes.
2. They don't dog their vehicles whereas they go easy on the cars engine and suspension with slower careful driving.
I'm partial to Toyota and Honda because I've found them to be reliable vehicles if you drive them right and keep up the maintenance.