550 miles and worn tires? I'd worry that it was beat...
I have 2000 miles on my original tires and they are about half tread. Unless he rode a lot on paved roads or burnt out constantly on rocks something seems wrong here.
Look inside the airbox for oil. If you see signs be sure to ask if he ever had the issue looked at by a dealer. At first dealers were replacing the labryth plate but that didn't solve the issue for most. We came up with the solution to remove the felt in the breather which solved the issue for pretty much everyone and after that Polaris released an updated breather valve. A search will lead you to pictures of what I'm talking about.
Check the brake pads as they may be stock still with that low of hours. If the tires are already in rough shape I'm sure the stock pads will need attention.
Check the wheel bearings by rocking the tires, mine started to develop a shake at 50mph around the 600 mile mark. Not the end of the world though, I still have my replacement bearings new in the box as the shake doesn't bother me to much yet.
Skid plates show action? Good, that means he used it! :drive:
I've heard of Ricochet skid plates getting built up with snow which can destroy CV boots so check that out.
With that many hours it NEEDS all the fluids changed. Front diff, Rear Diff and Transmission. (Obviously engine oil should've been done a few times by now.)
The ADC and brake fluid shouldn't need a change but you can inspect the resivour level by removing the front box (two clips on the inside and pull up) than remove the two screws under the headlight pod and take off the cover.
If the fluids haven't been changed, expect metal shavings on the magnetic plugs.
As far as price, don't know... Never considered selling mine. :trink4:
I hope the deal turns out good for you, I've loved my X2 since the day it was born.