Like most things - if it's too good to be true, then it probably isn't.
Everyone these days is looking for a deal. The fact of the matter, these websites are set up relatively quickly be people who don't know the first thing about boats or engines. However they do understand pricing, so the prices you see are always designed to be 'within reach'.
Better to buy from a reputable dealer and pay current rates than lose your hard-earned cash effectively for a picture 'borrowed' from somewhere on the net. I recognise one of two pictures from boats and outboards.