Blaster help.

first thing id do is take the seat cover off and if the airbox lid is removed, check the filter. if its dry and not oiled, it might be sand blasted to hell inside if they dont know how to properly oil a filter. other things would be compress. is it easy to kick over, hard. you want it releativly hard. but a rebuilds not bad. ask him what size bore its on. if he says .090 over then thats the last bore on the cylinder and if it doesnt last long, next rebuild you'd need a new cylinder or resleave it. ask how often they do gear oil changes just to see what your gettin into if they like never do it. other than look down the frame and check to see if its tweaked, cant think of anything else. you dont want a bent frame that will be hell to fix and if its bad, would mess up handling and whatever. if thats it in that picture, id say look under the engine to see if theres any cracks with oil leaking out cuz look at that oil spot lol.
 
check crank cases for oil, check compression. should be between 120 to 135 for a stock bike lowerer then 90 no good, look at the plug should be a cardboard brown, check chain sprocket and rear bearings by lifting bike in rear and trying to move the axle around. any play?? check front bearing push in and out on top of tire see if rubbers are all good any play?? ask about crank oil what they run how often they change it, anything you find wrong use as a bargaining tool.. good luck