my last car i brought privately had outstanding finance.
the guy told me, but as i was buying, he paid it off and showed me the paper work etc.
i personally wouldn't pass the full lump sum over and then waiting the seller to pay it off.
as above, pay directly to the finance company, or make sure he pays it on the day and it clears or get him to pay for it first and then you pay him.
i've seen quite a few without rays, but with GT pack.
for the sake of £5-20, i would get a HPI.
i can higly recommend experian autocheck £20, but i'll dig up a discount code for £10 off. it's just saved my back side, as the car i was looking at was CAT D, but looked fine.
i'm assuming you can haggle on sticker price too.
on the money saved, get some wide split rims ;-)