I wouldn't be too concerned about the dealership mileage, there are plenty of good dealers such as Andy at Euromotors or Dan from Motoxotica that will answer most of your questions over the phone and ship parts the same day.
Your trading for the FX right? I think I know who it is.
I would look for any signs that the bike has been abused or poorly maintained. Things such as stripped bolts, dirty air-filter or oil are a clear sign of poor maintainance, check the coolant, listen for any unusual noises when the bike is running. I like to put a wrench on several random bolts to see if the threads are clean or if any are loose. Take it through the gears and make sure it runs good, if the owner won't let you take a putt on it before buying, just leave the bike alone. After riding it look for any unusual oil leakage.
Do a search for fx470 and 470 and 02 470. You will find plenty of information on what has gone wrong on others bikes. Remember most of the posts on sites such as this comes from people who have problems, and are looking for answers. Very few people post just to say their bike is running great.
Finally ask about any updates (rollers, counterbalancer bearings etc.), and what kind of service the bike has received. You should have a good feel for the bike and if you don't feel like what he is saying matches the way you see the bike as having been maintained, walk away.