I've had Cat C & D cars in the past!! For a car that's only worth a few grand it doesn't take much to write them off!!
I looked at a 2004 Hyundai Coupe V6 a while ago for a mate. It was a Cat C. The salvage company that was selling it knew the previous owner that'd had the accident so had managed to aquire all the service history, spare keys etc etc which is quite rare!!
Anyways, the only damage it had was front bumper, headlight & passenger side wing were damaged, not even that badly!! It had about 50k on the clock & was mint other than the light damage. The salvage guy said the previous owner was paid out £4.5k. He had the spare parts there to do full repair at a cost of £200 for everything needed.
The car sold on Ebay for £2200. My mate was outbid at the last minute!!
Oh & my GTV was a Cat C. No accident damage, suffered water damage to the engine so had full rebuild in July 2007!!
The W reg fiesta i've been using for work was also a Cat C in 2006 but fully repaired, could hardly tell it'd been bumped, the only thing that stood out was a patch of crappy paintwork on the drivers rear 1/4!! other than that it was reeeeeeally mint!! only had 32k on the clock as well, I've just sold it & made £250!!
The short story is, don't let it put you off until you've had a good look at the car!!