You need to speak to a Real Estate attorney for this one.
One thing that may help you though, is if the buyer or buyer's lender requests repairs refuse to do them. Sometimes that may be enough for the buyer to cancel the sale (in the case of the lender required repairs, if they are not completed the lender will not loan) and make sure that you disclose absolutey everything with the property.
The purchase contract is legally binding & typically doesn't include a rescission period for the seller's change of heart, only for non-performance by the buyer so make sure that you agent is on top of the deadlines for contingency removals & that the buyer closes on time (if they are going to be even a day late closing, you possibly could cancel for that reason).
But why the sellers' remorse?