Beware that there *are* faked V5s out there, and apparently they're pretty damn good as well.
The only real way to check it is through the DVLA and to get it HPI'ed. I wouldn't recommend taking it on the face value that you've got a V5, especially if the engine/frame numbers look odd.
Maybe a word with your local Police? I don't know if they'd deal with this sort of thing or laugh at you down the phone - maybe one of our locals could comment on what would happen?
Out of interest as the HPI check is £40 and bike is only £300 anyone got any discount voucher codes? There was a place on the site to put one in. Not that I am tight or anything...
If one of the previous owners is now a policeman he should be able to verify if the info on the V5 when it arrives is genuine. The Dorset Constabulary stolen vehicle squad should have updates from the DVLA about any fraudulent V5s doing the rounds.
Sometimes local cop shops run "vehicle check" weekends where they'll check paperwork etc if you think something is dodgy. Might be worth seeing if there's one in your area?
Have a look at the numbers which are stamped on it now. If any of them contain LVLO then it's had a new frame no assisgned by DVLA ( the letters stand for Local Vehicle Licensing Office ) if the original could not be verified. If this is the case then providing you get the V5 then there should be no problems. Then again, if you're not happy now then you'll probably never be happy with it.......