The measure of damages is much more complex that it appears. The issue of damages on comperable sales is difficult because each piece of real property is unique. This type of question requires a detailed analysis of the breach to evaluate the damages flowing from the breach. The most common remedy sought is not money damages at all, but "specific performance" requiring the seller to sell.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
The contract generally has provisions for damages available to the buyer. The normal buyer's remedy is an action for specific performance to force the sale. The homeowner should hire an experienced real estate lawyer in the county in which the property is located to advise him or her on the best way to respond to the lawyer for the buyer.
Disclaimer: This answer is provided for informational purposes only, does not constitute legal advice, and does not create an attorney-client relationship. Actual legal advice can only be provided after completing a comprehensive consultation in which all of the relevant facts are discussed and reviewed.
You are not going to get those damages, and we would have to see the contract to advise as to what the damages might be other than specific performance being sought.
R. Jason de Groot, Esq.,