I bought my first bike with like 5k miles and sold with 11,000. Not a single problem. I had my second bike from like 8-15. Not a single problem. And my current bike I bought with 13k and its up to 16,000 with only a new manual cam tensioner(like 250 dollar fix <.< Not too hard to do on your own if you have time, and a problem with most of the years CBRs). My dad has a VTX1300 from like 02 or 03 with almost 44,000 miles and it runs like a dream
Taking good care of a bike usually means it will last a lot longer. Changing oil regularly, and regular PM are the critical keys. But take it with a grain of salt. With my CBR its a manufactorerererer screw up. And anyone can say anything on the internet. So ask the guy some questions about what he does, like making small talk. Find out if he is a gear head. Look into the garage(if its open) and see what type of tools he has and how organized and clean it is. Clean, organized, nice tools usually point to a gearhead. Look at his other vehicles too while you circle your 500r. See what kind of condition they are kept in.