@Jimmy Lieu, The main reason for a buyer to use seller financing is because they can not get access to money, usually due to credit, bankruptcy, or somehow over-extended.
The buyer will usually overpay for a property due the fact that there are no banks or appraisals involved. It's just 2 parties that make a deal.
As far as an answer to your #2 question: I would do interest only loan (say 7-10%) as a seller financed deal with a payoff in 3-5 years. Buyer overpays, puts $$$ down, and I now collect interest before my final payoff. If they are unable to refi, I foreclose via contract.
In response to your #3 question: The buyers of owner financed properties may have great jobs, cash, or income, but are unable to get a loan. That makes owner financed deals lucrative. The seller can name the price AND terms and the buyer either takes it or leaves it. Not very many NICE properties are sold in this manner. In this market, it would be tough to find ANY properties sold via seller financing. And many might have great jobs, but not enough cash for a good down. So the price is elevated to compensate for that added risk. It really depends on the parties involved.
For the seller it is a liquidation of an asset without taking a complete hit. Can be sold in an 'installment sale', see your CPA for that one as I won't try to explain it. Basically it's almost 'net' the same $$$ to the seller as renting without the headaches. Usually done by owners at end of career/retiring, but not always the case.
Hope this helped.
Alan