of human life, civil laws
determine that which is just. Now according to these laws it is just
for buyer and seller to deceive one another (Cod. IV, xliv, De
Rescind. Vend. 8, 15): and this occurs by the seller selling a thing
for more than its worth, and the buyer buying a thing for less than
its worth. Therefore it is lawful to sell a thing for more than its
worth.

Obj. 2: Further, that which is common to all would seem to be natural
and not sinful. Now Augustine relates that the saying of a certain
jester was accepted by all, "You wish to buy for a song and to sell
at a premium," which agrees with the saying of Prov. 20:14, "It is
naught, it is naught, saith every buyer: and when he is gone away,
then he will boast." Therefore it is lawful to sell a thing for more
than its worth.

Obj. 3: Further, it does not seem unlawful if that which honesty
demands be done by mutual agreement. Now, according to the
Philosopher (Ethic. viii, 13), in the friendship which is based on
utility, the amount of the recompense for a favor received should
depend on the utility accruing to the receiver: and this utility
sometimes is worth more than the thing given, for instance if the
receiver be in great need of that thing, whether for the purpose of
avoiding a danger, or of deriving some particular benefit. Therefore,
in contracts of buying and selling, it is lawful to give a thing in
return for more than its worth.

_On the contrary,_ It is written (Matt. 7:12): "All things . . .
whatsoever you would that men should do to you, do you also to them."
But no man wishes to buy a thing for more than its worth. Therefore
no man should sell a thing to another man for more than its worth.

_I answer that,_ It is altogether sinful to have recourse to deceit
in order to sell a thing for more than its just price, because this
is to deceive one's neighbor so as to injure him. Hence Tully says
(De Offic. iii, 15): "Contracts should be entirely free from
double-dealing: the seller must not impose upon the bidder, nor the
buyer upon one that bids against him."

But, apart from fraud, we may speak of buying and selling in two
ways. First, as considered in themselves, and from this point of
view, buying and selling seem to be established for the common
advantage of both parties, one of whom requires that which belongs to
the other, and vice versa, as the Philosopher states (Polit. i, 3).
Now whatever is established for the common advantage, shoul