undoubtedly, one of the most widely used agreements (contract) in real estate is the promissory agreement for purchase and sale, also referred to as a preliminary agreement, or an option agreement, among others. c) it should contain the characteristic elements of a final agreement, i.e., what is to be sold, transferred or otherwise disposed of, as well as the price, etc. as to this point, our recommendation is that you seriously consider verifying that the person signing as promissory transferor (or seller) is the owner or, in the alternative, has the authority of a power of attorney or that of a legal representative to be able to sign the promissory agreement. to establish the obligation (unilateral or bilateral) for the purchase and sale of a specific parcel of real property. [11] in view of the foregoing, it is of vital importance to be able to distinguish the type of agreement that is being carried out – a promise for purchase and sale, an informal purchase-sale, or an installment sale – since the rules to demand specific performance** thereof before a judicial authority are modified (or amended) according to the type of agreement concerned. **a legal action in which the court requires a party to a contract to perform the terms of the contract when he has refused to fulfill his obligations [1] compendio de derecho civil iv.