When on the other hand the gift is not disinterested but made with a view to a recompense, it is no doubt the best thing that a return should be made such as both parties concur in thinking to be what is due. But failing such concurrence, it would seem to be not only inevitable but just that the amount of the return should be fixed by the party that received the initial service, since the donor will have recovered what the recipient really owes when he has been paid the value of the service to him, or the sum that he would have been willing to pay as the price of the pleasure.