I'm part of a REI group that has trained us on how to make the presentation using tools they've provided (we bought).
I would go through the numbers with a Seller to show them all the Costs associated with selling their house and what their final cash amount could be. Let them know that they could spread out the capital gains tax by seller financing the cash amount to you over terms. Be sure to include the Dealer commissions even if you may not use them, and the other Mortgage, Insurance and Property Tax amounts they are responsible for until the property is closed on. They would only pay tax on the amount they received in a year instead of the entire amount (which could possibly push them into a higher tax bracket).
Show them how they are protected in the Subject-To sale because IF you fail to make payments on the mortgage, they will know about it immediately since it is still in their name, and in worst case scenario they would get the house back, but we never want this to happen.