What Cat D write-off means for you
Cat D was an insurers' write-off category used before October 2017. Cars now get Cat S for structural damage or Cat N for non-structural damage, and Cat A or B if they can never return to the road. A Cat D record means the car was written off at some point.
Ask the seller for repair receipts, and check the VIN on the car matches the V5C. Get an independent inspection looking closely at the structure, and make sure any repaired car is declared to your insurer. A Full Check at £9.99 includes write-off records.