definitely NOT a dealer. there are so many private sale Gen I and II's out there that you can steal either from a private sale. yes 20,000 miles wud be considered relatively high. really wudnt mean shiit to be honest with you cause they will go to a 100,000+ miles.
but the price difference between one with 5000 miles vs 25000 miles isn't gonna be all that much so common sense says to find one with lower miles.
ull have to decide which u prefer? the Gen I or II. I cud hav gotten either and price wasn't the issue. I decided on a Gen I cause there will never be another Gen I so it will always be a classic. I happen to like the look of the Gen I or the Gen II but its personal preference. the Gen II looks badass too and has many upgraded features and benefits.
make sure it has no cracks in the fairing. in fact, don't screw with anything that needs body work cause their are thousands of mint ones out there turn-key ready to go.
try to find one with some tasteful mods already. mods don't bring much value to the price of a bike usually but YOU gotta pay full price if u want em on ur bike which u will so save urself the money and spend a little more up front on one with tasteful mods already.
Check the transmission to see if it shifts smoothly, particularly second gear. inspect rotors too. look at bar ends to see if chewed up. mite indicate it was dropped so check fairing and make sure its original and not repainted.
buy an 2003 or later. less fuel issues. many changes. there are like 10 billion bikes to choose from 2003-2015 so jus steer clear of anything before 2003. make sure no rust in tank and look for rubber under the rear tail. chk the VIN yea snds obvious but many overlook it. clean title of course.
don't go to some ghetto to buy it either and get robbed for ur money. seen it happen dozens of times so buy from the suburbs.
to the oRg 
120K miles would be borderline high 
If you buy a 1999-2007 make sure 2nd gear is good. You should know what to look for otherwise.
