The first year the 6284 was availlable was in 2005, therefore at most the machine is only a year old. For that machine, which is only barely over a year old, to have 500 hours on it would be VERY suprising. Almost no one using a tractor that small will ever put 500 hours on it in one years time. Do you know what the guy uses it for, or did use it for?
Now the price seems about right, actually darn good considering the machine is only a year old and that a brand new one list for a little under 13K.
The tractor has a powerful 28hp CAT (Perkins) diesel motor, PosiTrac on demand 4wd, and is the best CUT built by Cub Cadet to date. Ask the owner if it has served him/her well. So check why so many hours, what it was used to do, and then jump on the tractor for that price if all the other answers don't cause red flags to fly up. Good luck.