Seller finance means you are paid over time, usually with a note. You are acting as the bank. Default, taxes, insurance, and what happens if payments stop all have to be written down. It can fit an owner who wants a price the cash number will not reach, and who can afford to wait for the money.
Subject-to and some lease-options leave the existing mortgage in the seller’s name while someone else lives there or takes over payments. Many mortgages have a due-on-sale clause. The lender may have the right to call the loan due. That risk does not disappear because a buyer is friendly. You should have your own attorney read any contract before you sign.
If you want cash and only cash, say so. Choose “Cash only” on the form. Creative finance is a tool, not a default we push on every house.