Last time i spoke to a lawyer about similar they said that writing "sold as seen" meant nothing at all in a court of law, as its so ambiguous.
As it could be said to imply that if looks fit for a purpose, then you as a seller are guarenteeing that it is indeed sold exactly as its seen, ie seen to be fit for that purpose.

I was told the ONLY way to avoid the "fit for purpose" obligation of the 1979 sale of goods act with regards to a car was to write "sold for spares or repair only" on the receipt.