Far too suspicious! Why not just buy another 335i, save up and mod as you go along and enjoy the satisfactiopn of its transformation. 335i values have dropped considerably so might aswell get something with higher mileage (even 20-30k on the clock) less money and peace of mind that you've got a legit car.
Yes we could all be wrong and that car could turn out a real bargain / deal however, the cons outweigh the pro far more IMO. You can get around the genuiness of mileage by doing a free check on dvla website (you'll need the car reg and Vin number / last MOT number) however, how will you ever check the paint work under the wrap....?? hmmm..
Now: E92 335D, Custom Cars Branded
Gone But Not Forgotten: E90 320D Alpine White