Section — Prümmer, Manuale Theologiae Moralis
1. On Merchandise and the Obligation of the Seller
292. Merchandise, or the object of sale, can be any thing estimable in money and belonging to the seller, unless a special prohibition of positive law is present.
It is said, 1. "any thing estimable in money," whether that thing be corporeal or incorporeal, such as a right of nobility. It is not lawful to buy or sell spiritual things for a temporal price, for this would be simony. The thing must be valued in money, because otherwise there is no longer a sale properly so called, but an exchange. Hence if someone gives, e.g., ten sheep for a horse, it is an exchange rather than a sale. These three contracts must be accurately distinguished: exchange, purchase-sale, and currency exchange. For if one thing is delivered for another, there is an exchange; if a thing is delivered for money as a price, there is purchase-sale; if one kind of money is delivered for another, there is currency exchange.134
It is said, 2. "belonging to the seller." Therefore the sale of another's thing is invalid; compare, however, civil laws which sometimes establish otherwise, as was said above, n. 213, concerning a possessor in good faith. Those laws can be observed also in the forum of conscience. It is not required, however, that the seller actually possess the thing; it suffices that he have it in expectation, e.g., grain which is still growing in the blade. But nearly all modern laws prohibit an heir from selling a future inheritance, because such a contract is considered shameful, as inducing a desire for the death of the testator.135
It is said, 3. "unless a special prohibition of positive law is present." For certain things cannot be sold while preserving the common good, e.g., certain weapons, poisons, or even precious paintings, etc.
134 To these contracts of exchange and currency exchange, as also to the very common instrument which is called a cheque or bill of exchange (Wechsel), the same principles are to be applied which hold for purchase and sale.
135 German Civil Code §§ 310, 312.
293. Obligations of the seller.
The seller must not demand an unjust price, concerning which there will be discussion below.
By natural law the seller is always bound to disclose to the buyer the substantial defects of the thing to be sold. The reason is that otherwise the consent of the buyer will be invalid, and consequently the entire contract invalid. Positive laws in some cases admit the so-called redhibitory action (Wandelungsklage) if a defect of the thing was concealed. Those are considered substantial defects (Hauptmängel) of the thing which render it notably useless for the primary purpose known to the buyer. But with regard to accidental defects a distinction must be made: if the buyer expressly asks concerning these defects, the seller is bound to answer according to the truth, or at least to decline an answer by saying, e.g., I sell the thing in the state in which it now is. For then the buyer can provide for himself; if he does not do so, he will have to bear the loss. But if the buyer does not expressly inquire concerning these defects, then the seller cannot by frauds induce him into error and thus cause him great damage; therefore he is bound to disclose entirely hidden defects which notably diminish the thing, but he need not indicate defects which any prudent person can easily detect.
St. Thomas teaches excellently concerning this matter:136 "Concerning a thing which is sold, a threefold defect can be considered. One is according to the species of the thing, and if the seller knows this defect in the thing which he sells, he commits fraud in the sale; hence the sale is rendered illicit.... Another defect is according to quantity, which is known by measure; and therefore if someone knowingly uses a deficient measure in selling, he commits fraud and the sale is illicit. Hence it is said:137 'Thou shalt not have divers weights in thy bag, a greater and a less; neither shall there be in thy house a greater bushel and a less,' and afterward it is added: 'For the Lord abhorreth him that doth these things, and He hateth all injustice.' The third defect is on the part of quality, as if someone should sell a sick animal as healthy; if someone knowingly does this, he commits fraud in the sale, whence the sale is illicit. And in all such things one not only sins by making an unjust sale, but is also bound to restitution." As is evident from the example adduced of the sick animal, the Angelic Doctor speaks of a quality redounding upon the substance; but if there is question of a truly accidental quality, there is no grave obligation of restitution.
The seller is bound to deliver the thing physically, or at least morally, the same as that which the buyer intends to acquire. I say, however, at least morally the same; for even if the thing given is physically not altogether that which the buyer thought he was acquiring, nevertheless, if morally it is the same, i.e., almost equally good and useful to the buyer and worthy of the price offered, then there is at least no grave injustice.138 E.g., when guests ask for Moselle wine in an inn and the innkeeper gives them wine almost equally good which, however, was not grown on the banks of the Moselle, he does not seem gravely to injure justice, provided, however, that he does not exceed the just price.
The seller is bound to deliver the thing sold to the buyer in the state in which it was at the time of the sale. Civil laws are wont to establish, or the contracting parties specially determine, whether the seller or the buyer receives the fruits of the thing before delivery; who ought to bear the expenses of custody; for whom the thing perishes, etc. All these statutes are to be observed faithfully.
136 S. theol. 2, 2, q. 77, a. 2.
137 Deut. 25:13.
138 S. theol. 2, 2, q. 77, a. 2 ad 1.
294. Scholion. On diminution of weight or measure. St. Alphonsus139 asks: "Whether one is excused [from injustice] who uses a diminished measure in order to obtain a just price which otherwise he would not obtain because of an unjust rate or an unjust monopoly of buyers? Lugo, Laymann, Palaus, and Sporer with Soto, Valentia, and Toledo, and the Salmanticenses with Rebello, Salas, and Dicastillo affirm this as very probable. The reason is that then he justly redeems himself from vexation." These things, however, are to be understood with a grain of salt and in our times can very rarely be reduced to practice; for it is said in Sacred Scripture: "A deceitful balance is an abomination before the Lord."140 Especially, the excuse often brought forth by merchants is not sufficient, namely, that they cannot withstand "competition" if they do not diminish weight and measure. For no injury is inflicted upon them by the buyers. Nor may they say that the weight, even thus diminished, corresponds to the just price. For although this is true absolutely, nevertheless it is false after agreement has once been legitimately made concerning such a price and such a weight.141 They can, however, defend themselves against other "competitors" by accusing them of illicit machinations, or unfair competition (unlauterer Wettbewerb, concurrence déloyale). Such diminution of weight or measure is lawful only: a) if universal custom so bears and this can easily be known by the buyers; b) if buyers by unjust means, e.g., by so-called "syndicates" or boycott, compel sellers to a truly unjust price, because then the sellers can defend themselves.
Rules to be attended to by the confessor. Almost innumerable are the frauds which are wont to be committed in the sale of things. To discern whether from those committed there arises a grave obligation of restitution, the confessor should attend to three things:
a) whether the damaging is truly, formally, and efficaciously unjust, and this in grave matter;
b) whether the thing sold is at least morally the same as that which the buyer thought he was acquiring;
c) what the custom in force is in such a sale.
139 Theol. mor. l. 3, n. 822.
140 Prov. 11:1.
141 Thus also Billuart, De contract. diss. 5, a. 3.