Purchasing a used car can be a risky decision. Your friend might actually tell you not to buy a used car from someone who can’t show you pieces of evidence about the routine maintenance services for the vehicle he’s/she’s selling. Those pieces of evidence will tell you how the previous owner took care of that car.
However, you don’t need to ask the seller about those receipts. There are other ways that can tell whether or not such car is worth the price.