With regular maintenance and proper storage, a good splitter will last a long time.
I've got a 10 yr old, 34T Brave (Iron & Oak) that I've never had any issues with. I only use it around 100 hrs a year and change the engine oil every 50 hrs. I store it inside, only use E free fuel and drain it at the end of the season. I bought it used, three years old, from a guy who is anal about maintenance.
I have neighbors with newer splitters that are stored outside, some covered, some not and rarely, if ever, have the oil changed. For some reason, they have to rebuild the carbs every year and are constantly having problems with their splitters.
If you can verify the maintenance on the unit, $500 might be a decent deal, at least in your market. It really depends on the hours, maintenance and storage. Without actually seeing the unit, it's hard to say.
Around where I live, a 10 yr old 22T Huskee, would have to be in exceptional shape to bring $500.