The two times I purchased a used car, I changed the oil right away as the oil was quite dark, so I can't understand a person buying a unknown used car and not doing the same. I changed the corroded battery terminals on the first and cleaned and lubed both cars connections. I sprayed all the door hinges and locks. I I used the first for two years and sold it for the same amount as I paid for it including maintenance, but not insurance. The second one I lost $7.000 over 6 years on depreciation and $3,000 on maintenance. I actually paid more on insurance on the second car than I paid for the car itself. All maintenance was at the dealer who replaced two sticking rear calipers under warranty, but not the destroyed rotor or the brake pads, hence the higher relative maintenance. I actually had to prove that the second caliper was sticking using an inflared thermometer reading on arrival at the dealer showing the 300°C reading before they changed it under warranty.