I've had accident damaged cars in the past and had them professionally repaired by trusted sources. The pros are that you can usually get them quite cheap, and sometimes with only very minor damage. The downside is that as mentioned above, their re-sale value tends to be much lower than straight cars.
Cat C usually means there has been damage that is more than cosmetic, and unless you know who has repaired it, I would definitely advise that you find out exactly what the damage was and get it checked out by an independent inspector, for safety and quality of repair.
You may be onto a good thing, providing all the boxes have been ticked in respect of the repair process. The last thing you want is two cars stuck together, so just be careful!!