Just ask if the motor and suspension has had any work, if he has any receipts to show for it, I've got an 05 RM, which I feel is the funnest bike I've owned, but like I said before, the YZ is a great choice also, my personal preference lies with the Zook though. But while either choice would be a good one, you need to decide if you want The YZ that's maybe not as good as what the RM was built for(track) but may be more versatile, or the RM which is a suited for a more aggressive riding style, don't get me wrong, I trail ride the RM and it's ok, just can be a handful sometimes. As long as both bikes are in good shape, don't think you can go wrong here.