the blue book on that bike is almost 5k retail, so if he is including tax, it is a good deal. Keep in mind, that you can almost certainly get a better deal if you are willing to hold out for a private party deal.
Try work them down on the price. I got a 2002 750 Dark with 960 miles for $5000.00. Mine was also visibly unflawed and mine has both discs in front.
It sounds a little pricy for a 02 with that many miles. If they won't bring down the price ask for gear or accessaries for the bike. That comes out of another part of their pricing so they can often do that.
I wouldn't take it AMS in Texas had an 02 brand new and they were willing to ship to my house for free for $5000 plus taxes... I would check them out and see if they still have it. It was an 02 620 dark with single disk.
We paid 5K for my wifes 02' 620 dark, right before Christmas. I figure we could have done better, but after all the shipping, and not really knowing what you get untill it arives...we opted to spend a little extra and get a bike we knew had been taken care of, and was in excellent shape. ;D