Some early '02 bikes were shipped with a defective igniter, but those are pretty much all replaced by now. At any rate, Triumph is aware of the problem and will usually replace the igniter free if you happen to get one.
Other than that, there have been no real flaws to watch for.
Of course, look closely for signs of abuse.
Worn out hero buttons on the footpegs (or ones that are so new they have to be replacements), bent/scraped frame parts, Headlight lens fogged by sand impacts are a few obvious problems.
If the oil has not obviously been freshly changed, give it a sniff to see if it has a burnt or gasoline smell.
If the teeth on the rear sprocket are worn to a hook shape, chain and both sprockets should be replaced. Try to get the seller to do it, but it's not all that expensive if they won't.
