Also know as "Seller May Carry" terms. Typically interim financing of 3-5 years with a 15% to 30% down payment providing time for the buyer to get a conventional or FHA, VA loan and pay the seller off at that time.
For more information: http://arizonahomesland.com/sellermaycarryhomes.html
Jeffrey Masich, Realtor, GRI, MBA
Arizona homes and land for purchase or sale
In general, this owner seems to be advertising that they will extend a loan to the new Buyer if the Buyer has 20% of the purchase price to put as a down payment.
Or, to put it in numbers - if you agree that the purchase price will be $99,900, then the Seller expects the Buyer to pay him $19,980 at close of escrow, and the seller will extend a loan for $79,920. The terms of the loan are negotiable.