Thats got total scam written all over it. If it is legit then i'm sure the seller would be happy for you to do all the necessary checks, home visit/inspection, check documents etc etc. Could be a Cat D repaired i suppose? If they say no to any of these requests then step away....if it looks too good to be true then most likely it is!
Just had a quick flick through Pistonheads. Theres a 56plate on there with simular mileage up for £16500 so I suppose it could be a listing mistake?