Sold as seen means fuck all! If the car was not fit for purpose, ie. in this case sold as road worthy when in fact it isn't you have a case for getting your money back. I've bought a car as a trade sale, sold as seen etc. and 10 days later the engine went. Took it to an independent garage and they said it is due to a problem the seller would have known about. After a few phone calls I got my money back.

Having said it all that it pays to do a THOROUGH inspection or use someone who knows what they're looking at, especialy on things like RSTs, but hey, hindsight is a wonderful thing lol