#6: basically the lender will decide on whether to approve the short sale (a price reduction from what the seller owned) based on the affidavit.
#10: Seller can cancel the sale agreement any time if the house went to foreclosure and taken over by the lender.
#13: If you and seller provided missleading information, you and the seller will pay the lender any loss, including the difference between the price of short sale and the mortgage the seller ownered.
You have no choice but to sign the affidavit if you want the house.