|Did the buyer sign a contract? If there is not a contingency for their own appraisal coming in lower, they cannot use that for a reason to back out of a contract. They need to compare comps and see what the "legitimate" difference, is AND then decide if the seller wants s to renegotiate.|
The seller can sell at any price reasonable they want (bidding wars), it's not up to the buyer to determine the price they feel they want. If the buyer gets cold feet and now wants a lower price, it doesn't work that way onmce a contract is signed. They can lose all the money holding the property in escrow.
Basically, an honest appraisal goes by the nearest set of 3-4 comps of the same house, square footage, same age and type of location. This has nothing to do with that. They want the house cheaper and found an appraiser to give them the lower number. How did this appraiser have access to the property? Did the seller let them in? Truthfully doesn't matter. I'd call their bluff, keep their deposit and let them walk. It's a seller's market right now.