If one party backs out of the deal, what can the other do?

When there is a Purchase Agreement in place, it is binding on the parties. When one party backs out, there are usually terms that allow the other party to enforce their rights. The agreement usually contains the remedies of the aggrieved party (contractual remedies) or they can rely on the common law or the law of equity. Whatever the case may be, the agreement is in writing and the terms thereof are fixed.