From what I've gathered after much reading about these bikes on this forum.
2 main issues seem to pop up.
1. The airbox can leak. The ring that holds the boot to the airbox is made of plastic and is basically a POS. If you buy this bike, check and see if he put a metal ring on there or if he siliconed the airbox to boot area.
2. Most people don't like the stock Mikuni TMX carb. They have a lot of issues attempting to dial in the jetting. A lot of people pick up a Keihin PWK off of a 99-01 CR250. Personally I have a TMX on mine and it runs fine. JD jetting sells a kit to dial in the TMX's very well.
This year motor is generally considered stock tuned more for mid range to top end performance. I ride my '02 in the woods all the time and it pulls hard through the whole RPM range. Mine has a lot of bolt on mods that might have helped that though.
Overall I'm very happy with it and you won't be disappointed.