Today, they normally demand upfront payment, so the buyer has to borrow from a bank. These loans are extortionate. The buyer normally pays the bank back about double what he borrowed, over about 30 years.
Instead, the buyer could offer to pay 50% extra on the cost of the house. But he will pay some of it in installments over 30 years. The bank gets nothing, and the buyer and sellers both make huge savings.
It wouldn't be suitable for every sale, but it would for many. So why don't people do it? Is there some legal restriction where only the banks are allowed to do this kind of financing?