Hello Lee,
Couple of important points:- What damage has been caused to this vehicle to render it a Category C "write off" (beyond economical repair) by the insurers?
If there isn't any apparent body damage, has it been flood damaged for example and just cleaned up? Who is selling it and why?
Have they acquired it simply to sell it on, or are they now selling it on because they now know it's damage history and just want to get rid of it?
So, you need its claim history, and an assessment of the current state of the car and whether it is driveable/able to be tested and assessed. Also (important) - what year is it?
Hope this helps a bit, but it's really doing your homework time, and if you cannot get the honest answers then I guess you walk away, or perhaps take a brave chance.
Kind regards,
Gareth.