To sell a house quickly, it must be attractive and so should the terms. By fixing your home to present it in the best light and offering flexible terms as well, you have in fact given your buyer an "offer they can't refuse." When offering your house for an all-cash purchase only, you limit your market. If you're flexible on the financing terms of the property, you increase your pool of buyers and thus the demand for your house
Let's discuss the mechanics of the owner financing, which is different if the seller has existing financing on the property.