the SX model of XB series also referred to as the CityX or City cross. i own 3 of that model and they're very desirable, very comfortable, simple motorcycles that have a loyal following. check the VIN to confirm that it in fact is a real SX and not a clone. SX bling includes cross-braced bars, X airbox protector, cityX badging, transluscent bodywork in choice of 4 colors if you include the rare limited edition, 984cc motor, color keyed cheese grater on some colors, hand guards, headlight grille. the price you mentioned is way below fair-market value IF the bike is decent both mechanically and cosmetically. due to it being 11 years old figure on spending a minimum of $500 to freshen up the tires, brake system, battery, all fluids, all adjustments, idler pulley bearings and a few other trinkets with that $ amount based on you performing the work.
lastly.....if it was bashed, trashed, raced or abused steer clear. if the seller truthfully reports a decent service history and rode it reasonably it should be in nice condition. if it has been thrashed walk away. air-cooled buells don't respond well to excessive heat conditions but there are remedies to potential problems such as avoiding stop and go traffic whenever possible...a right side air intake scoop sytem.....under-seat insulation kits....and a fully functional fan. if you observe oil mist anywhere on the rear cylinder area and/or the fan then the fan is on death-row and MUST be replaced. knock? spoken of with some 2007 models and caused by a knife and fork con-rod big end pin bearing. not that common but they are out there.
