Well, for a stunted bike I wouldn't even ride the thing, let alone consider buying it. Sportbikes are like jets, there is little to no tolerence of critical parts that fail at speed. Simply having a peg come loose or having the throttle stick a little could kill you when you're going at a good pace. Frame or suspension damage, engine malfunction, frozen brakes or damaged tires offer a much more grim scenario even. The body is a temple and so is the bike that carries it.
However, I bought my F4i from an older guy that simply wasn't a good rider, who had tipped it over twice (once at around 15 MPH and once at 5 MPH) leaving minor cosmetic damage that he did not try to cover up. The bike was a year old, had 1,500 miles on it, and was only $5,000. In this situation - seeing the bike first-hand and riding before buying - the bike was a really good purchase as it was essentially brand new off of the showroom floor but with some scuffed plastic, a hairline fairing crack, and a broken mirror. I fixed the minor problems and nitpicked over the bike myself, leaving me with essentially a new F4i with lots of higher spec aftermarket bits for under $6,000.
How is a stunted bike different? With 14k miles of abuse (or even 3k per se), who knows what lies beneath the paint or the metal casing. The frame could be twisted, the wheels could have oddities, the tranny could be on the verge and the suspension could be nearly shot. Aluminum does weaken over time of use (like with a bicycle frame) and so there's no telling of what point the frame is at, or anything else. While it's very unlikely that anything would really break cleanly, the deterioration could lead to a fatal malfunction. Stunting is probably the best way to rapidly deteriorate a sportbike. Think of it this way: for $3,500 you could probably find a good SV650, a really nice Ninja 250/500 or even an excellent condition CBR600 F2 or F3. Be patient.
**As an added bit of humor, the older guy that was a terrible rider that I bought my bike from was selling the bike because he was scared of it and said that he was going to buy a new Harley VROD to replace it! Hmm, yes a bike that has a more powerful engine yet doesn't handle nearly as well is a wonderful choice. That's like buying a muscle car because your Porsche scares you.