Can't trust miles because of speedo replacements. What do the handle bar grips look like? How much wear on the footpeg plates where boots would rub on them? Flip up the seat, what does the frame look like where the seat rubbers rest on it? Unfortunately, the best indicators of wear are internal, and I don't know any sellers who would let you take a bike apart to look at the splines, or the frame loop under the rear cowl.
As far as market value, it's hard to say. I see these bikes go for anywhere from $7-800 to over $3K. I guess it depends on how bad the seller wants to get rid of it and how bad the buyer wants it. One thing for sure, a seller will never tell you that you're offering too much.