Qitzur Shulchan Arukh 62:1
סִימָן סב – הִלְכוֹת מַשָּׂא וּמַתָּן
Chapter 62: Laws of Buying and Selling
One must be very careful not to take advantage of his peer. And someone who does take advantage of his peer, whether the seller takes advantage of the buyer, or the buyer taking advantage of the seller, is defying a prohibition. As it says, “‘If you sell anything to your neighbor, or buy anything from your neighbor’s possession, do not cheat one another.” (Vayiqra 25:14)
This is the first question that they ask a person at the time they bring him to justice [after his passing], “Did you conduct your buying and selling with trustworthiness?
C.f.: Choshein Mishpat 227, Shabbos 31a, and also see Orakh Chaim 155, and Yoreh De’ah 246.
The Qitzur opens with a discussion of how evil ona’as mamon, cheating is.