It's up to the seller to disclose whatever, however they like...buyer beware etc. No legal obligation. Harder to not disclose a cat c because it's printed on the v5 after the cars had its identity check from the dvla.
Some crash repaired cars are brilliant, others are death traps, but that also applies to cars that are not on the register. I've seen cars involved in fairly heavy accidents bodged back together and sold on to be the new owners problem. Morals etc tend to go out the window for the sake of a couple of quid theses days.
I quite fancy a trophy but they just arnt worth what they appear to be advertised for I got my 197 for less than I've seen trophys advertised for.