a hpi check can't guarantee the mileage it has been proven many times that they have got it wrong best way is check the car out will be pretty obvious if the mileage is correct seat wear and many other things to look for
oh mine had 2 previous owners with 22k on the clock at 4 years of age
the service history will be your best bet,for example Audi keep the records of all the work carried out at there dealerships so you can ring up and ask for a printout of all the work done to the obviously they record the mileage when carrying out any work
HTH