HPI it on the VIN, this is REALLY IMPORTANT, i bought a Porsche 944S2 a few years ago and HPI'd it on the plate on the car - clean, then HPI'd it on the VIN, outstanding finance!!! The car had had a personal plate, which the previous owner had put onto retention prior to selling the car, and had got the correct age related plate from DVLA (new plate on the car) the new plate had no finance record as was linked to the old plate and the VIN!! He hadn't paid off the finance, I pointed it out to him and he cleared finance, got letter from finance company saying clear, deal was done
and three years later same thing happened with a 911 at a Porsche main dealer, except this time the car was on a stocking plan, again no drama, was cleared before I paid for it. But after this I always HPI the VIN as well as the plate.
HTH John