Standard for handling appraisals lower than contracted sales price

[Allison Park]

Hello, 

I am selling a property and it has appraised lower than the contacted price by $9,000.  In this case the buyer is asking for the seller to concede the difference between the sales price and the appraisal price.  Is this standard?  Can the seller avoid this buy putting in the contract that the buyer agrees to pay the difference?  Any other ways to handle this?