I look at things different than a lot of other people (somewhat synical) cause I want the mosty for my money. Records and service manuals can be false. Speedos can be switched out and lets face it people lie. With that said lets look at buying a bike. the first and last thing is that no matter how much or little you pay for a bike the only one who needs to be happy about it is you. You will always encounter those who "CLAIM" they could have gotten you a better deal. If that was true then where were they when you were making the deal?
When looking at a high milage anything do the math first, how many miles per year does it average out to? What is the riding season like for the area, if it is Florida then it might be all year, if it is New York then it is seasonal (unless the seller is really hard core and loves the cold). If it is Florida then milage is spread out, could be a lot of stop and go type traffic in hot weather (more wear). If it is New York it could be a lot of distance riding getting put on in a short time.
Look for blatent signs of wear, the seat the grips, floorboards and around the ignition key switch. Look for wear marks on the lower area of the tank from were most people squeeze the tank with there legs and a key spot, the lower front forks! Do they look sand blasted, pitted and worn? These are all good indications of how well the bike was taken care of.
Do your research as well. As others have said some people just think there stuff is worth more than others. I live in Jacksonville, Fl and I see it on Craigslist everyday, someone will have a Harley of some type on thier with aftermarket grips, pegs and seat and all of a sudden it is a CUSTOM Harley and they want 3 grand more than you can buy a new one for. Also don't get chrome eyes (my brother has them), Chrome looks great but has no standing on how the bike will perform. On trade ins chrome is only worth 10% of the original price...ie; $3000 in chrome = $300. my point is don't be fooled by it. Look at the real bike, is the oil clean? Is the brake fluid cloudy or clean, what do the brakes look like, any dry rot on the tires, what kind of tires and rims are they billet, cast or spoked (I hate spokes, look nice, hard to clean even more of a pain when they start coming loose). If the are spoked do the tune test, run a thin screwdriver handle around the spokes and make them sing. They should all tink nicely any thuds and odds are the spokes are loose. Lift the seat and check out the battery, is it clean or coroded, how old is it.
The point of all this is look the bike over well, if you are unsure of how to do it take someone with you. Find out what dealer the seller takes it to then take it to a diffrent dealer (he has friends at his dealer who may lie for him. Remember I am synical and want the most for my money).
Either way be cautious spend your money carefully and there is nothing wrong with high milage rides as long as they where taken care of.
Good Luck and whatever you decided remember only you need to be happy with the deal.