For even in sales this is plainly what takes place; and in some states there is no recovery by law in voluntary contracts, as it is held that when you have given a man credit, you must conclude your bargain with him in the same spirit in which you began it. It is held to be fairer that the service should be valued by him who is trusted than by him who trusts. For most things are differently valued by those who have them and by those who wish to get them: what belongs to us, and what we give away, always seems very precious to us. Nevertheless, the return to be made must be measured by the value which is set upon the service by the receiver. But perhaps he ought to put it, not at what it seems to be worth when he has got it, but at the value he set upon it before he had it.