Sounds like my bike when I first test rode it. Has that bike sat for an extended period? On my first test ride the bike bogged and pinged, sounded like it was running on three cylinders. That's probably bad gas/dirty carb orifices, if it has sat for a couple months. I fixed by: draining gas for use with my lawn mower, cleaned the carbs, reset the pilot air screws, sync'ed the carbs, RE-jetted/shimmed/float height and selected a new exhaust.
Runs like a gem.
1999 cons: single smiling headlight...a personal preference...some like the dual lights on 00-03 models. I think overall the 99 is a solid mount from what I've seen, but then, I own a 2000.
Certainly ask to have "your mechanic" check it out. You should check its transmission for normal shifting and stress each gear to be sure it doesn't pop out under load. Check for exhaust smoke. If the top engine components (plastics, wiring, vacuum hoses) look in good shape, nothing's missing, and a compression check returns 150+ PSI per cylinder on a warm engine, it's probably in decent shape. Pay whatever the market will bare. $2K is more than fair, but express reservations about the running condition and haggle.
], now give me mine back!! Ahh, what a sweet ride. 
