You mean like an assessment overview?
It's often the mods that offer hints as to how the bike's been run. A strictly OEM model in that age range would be unique imho: the closer you get to OEM, the better. That is a generalization.
Aside from engine internals (which can be difficult to discern at tire-kick inspection), much of the peripheral stuff can be (and should be, on purchase) replaced: tires, levers, hoses, cables, grips, cowls, fluids, brake pads, even the rotors. I'd look at the current condition of sprockets, chain, obvious stuff like oil stains on metal, to determine how well the bike's been kept. Listen to the diff bet clutch in/out - that rattle... It's kinda hard with Busas, cuz many owners keep up on the maint and still run the bike aggressively. On the other hand, it's a Busa - it likes to be run hard. Maybe even prefers it.
Of course, if you can talk the seller into taking off both fairings, that'd be nice, give you a better look. And maybe if they were willing to let you pop the hood and look at the air filter. Reminds me of dating: it's a little easier to have a peek under the sweater to see if everything's real and if cuffs & collars match on the third date than it is on the first.
I'd also recommend researching the particular year of the bike in your crosshairs as there is a wealth of year/model specific data (things to look out for) right here on this site. (e.g., not ALL Gen 2's are ABS outfitted).
I was gonna say check the width of the chicken strips as an indicator, but I'm not sure that's good advice. Someone running the bike to its limit tends to take care of the other components (cuz, you know, they're related), but on the other hand, a squared off tire that looks unused at the edge might also be a sign of neglect.
You mean new (to me) maintenance?
All of that can be skipped along with the understanding that any of it could fail without notice. Which is why I service/replace a whole bunch of stuff on a new-to-me bike. I wanna see it for myself, wanna know EXACTLY how old the brake/clutch fluid is, what kind of oil is in the pan, blah, blah, blah.
Hope this helps