if everything says 5door but itss a 3 door then somthing is amiss and the owner should get it sorted out. ask them why they are advertising a 5door when its clearly a 3 door. if you really like the car then say you will buy it subject to a clean hpi but if there is something wrong you expect them to pay for the hpi.(check all numbers on the car and that they tally up with the hpi record, and look for signs of tampering) if they decline your offer then they have no confidence in the car they are selling and its time to walk away.
for me the alarm bells would be ringing so loud that i would run a mile. sounds like a ringer to me, walk away plenty more out there