Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos)
By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
First Section – the Positive Commandments
67. It is a positive commandment to judge business matters according to the ways of the Torah
meaning, there are situations between buyer and seller where the sale should stand and situations when it should not go through. It is a Torah commandment to judge them according to the laws of the Torah. A specific commandment is stated in a specific section in Vayikra (Leviticus) 25:14, "If you sell an item to your friend or sell an item to your friend," because this is a constant thing for people to do. It is impossible for a person to live one day if they are alone. Land is acquired through money, contract, or proof of ownership. Items and animals are acquired through pulling towards one's self, and, of course, through lifting the item or the like.
This applies in all places and at all times.