HPI check is ok, the National Mileage Register is a load of bull****.
I currently have my X5 for sale, and lost a buyer this week because "my HPI check revealed the mileage has been tampered with"
Reason: in October last year, some idiot at the dealer where it was being serviced entered 27,000 instead of 37,000 miles, then IMMEDIATELY on the same day corrected it to 37,000, but the initial input stood and this put my buyer off.
Now, I have cleared this up with HPI/NMR, but it has still left a very unpleasant taste in my mouth as my 'buyer' is no longer interested as he feels there must be something dodgy going on.
I am not a happy bunny, partly because the buyer is just being an idiot (he also said there was an alert due to a number plate change - well done Sherlock, it has my plate on it!) but if HPI are going to record this information then they must do more to validate its authenticity rather than ruining people's chances of selling privately through nothing other than a data input error.