That is true, but in terms of leverage for the seller:Yes but you're only getting interest on the downpayment, and you are foregoing interest on the amount that is owed to you.
If your buyer is creditworthy he can go to a bank and get a loan. If the reason he wants seller finance is because he can't get a bank loan, that should worry you. If he is trying to get seller finance as a way of paying no interest on the loan, then you should understand that you are losing that interest. You could be earning 10% interest on that money, the same 10% that he would be paying for a mortgage.
If a bank finances a house, the interest is all the benefit they get from the loan. If the seller finances the house, even if they didn't get any or a lot of interest on their money, they still get their property sold. If it's the buyers market, then this arrangement might be beneficial for the seller as well. We in fact tried this once and due to the very unfortunate fact that there was at the time a decent demand for properties in that particular segment, our nice proposal was declined as a buyer with cash in hand arrived and took the property, so it was the seller's market more or less at that time.