I made up some stats because I don't have a source of such data, and I'm looking to find out whether they're plausible and self consistent. If not, please correct them. They needn't be verified or actually sourced from a study, personal experience should suffice. This is for a question as to whether it's worth it to buy a used car after selling your own used car. A car's reliability decreases by 5% for every 30k miles. Its selling (you to buyer) price goes down by 30% for every 30k miles. Its buying (you from dealer) price goes down by 15% for every 30k miles.