Choosing the wrong lender
Sellers want/need the assurance of closing.
If your mortgage is through Bank of America, Chase, Wells Fargo, or any of the other 11 biggies, you are rolling the dice. The seller knows there are three elements in the process of these banks that make the outcome randdom and PUNITIVE for the seller and buyer.
A buyer REALLY needs to listen to their real estate professional. It matters not how 'super' your agent is, if you are rolling the dice with a big bank, you are on thin ice.