My understanding is that the seller must answer honestly about known defects when asked BUT is not required to point out any additional faults if the questions have not been asked.
BUT I would always have a used vehicle thoroughly inspected by a qualified workshop especially one that specializes in the particular make/model you are considering as they should know where to look and known faults.
You need to make inquires as to whether there is any finance owed , clear title, crash history and the stolen vehicle register plus service history before handing over your hard earned cash.