Buydown
  
Mortgages can be written with a buydown as part of the financing. This involves the seller helping the buyer to lower the interest rates for a period of years, or even the whole loan.
To do this, the seller puts money into escrow to make payments alongside the buyer, and lower the buyer's portion of payments. It can be done as a way to sweeten the deal on a hard-to-sell home, or in a slow real estate market. This method lowers the buyer's monthly payment, which makes it easier for the buyer to qualify for the loan.
Say you're selling a fixer-upper, and the only interested party is this sweet young couple, long on dreams...but short on qualifying work history to get approved for the mortgage.
You as the seller can put money into escrow to make the payments more manageable for them, and entice the bank into making the loan. It might cost you to do this, but it might be preferable to being stuck with a house you can't sell.