Did you know you can now get closing insurance when you sell your home. For as low as $99 you can be insured for up to $25,000 in the event that the buyers don't close. This will cover the cost of mortgage payments and other costs that you may have if you have to carry 2 homes.
There seems to be a growing trend of buyers being approved by the bank and then just before closing, the bank won't give them the mortgage money. This can happend for several reasons i.e. change in credit rating, large purchase before closings, loss of employment, etc. It's better to be cautious and prepare for the unexpected.