More than the price that can usually be negotiated in my world is the condition. Never buy an engine you cannot run and properly check it out. You want to go over all his engines and select the one with the highest compression and best overall run quality. Too many used engines are sold that are really just boat anchors. Once in awhile you are fortunate to personally know a person with a ton of integrity and product knowledge. That overcomes the need for evaluation but they are not all that common. Perhaps I should say almost rare. Sometimes you can find a rustout if they are in your area with a really good engine as well. Selling off what you do not need may give you an almost free engine. My kind of deal.