Buying a second hand motor? You probably know it is fraught with danger and uncertaintly, especially when buying privately where there is no warranty (outside of a manufacturers i.e. 3 years old of less), and you have no 'come back' if something goes wrong. Based on this I'd advise you buy from a dealers.
Whichever route you opt for there are some important steps to take to make sure your money is looked after and that you don't buy a duff aka 'Lemon'.
One such step is to run a history of a car for free check with a firm like My Car Check or CarVeto. There are specific steps to take here. The video below will outline one of them.