Overcharging
There is a Pasuk in Parshat Behar that commands us, לא תונו, which means that we must not aggrieve our fellow Jew. In this instance, it is referring to money matters.
This commandment warns us not to cheat people by overcharging movable items. There is a built in limit as to the profit one is allowed to make.
Generally, there are numerous products that have an established rate that the public is charged. A Jew is not allowed to make a profit of more than one sixth of this rate. The term for one sixth is “Shtut.” This is meant to prevent taking advantage of the consumer.
This is not the case when discussing real estate deals. The principle is, אין אונאה בקרקעות, that there is no such thing as overcharging when it comes to land.
This makes a lot of sense, as there are many times that a particular property is exceptionally valuable to a specific individual. There could be sentimental value involved, or perhaps that person already owes adjacent properties, so that paying above the market value, is worthwhile to him.
It is interesting how the Torah itself has regulations protecting the consumer. We are never allowed to take advantage of other people in any way. There are always temptations when it comes to money matters. This is why the Torah sets the standards as to the proper way to conduct ourselves in all aspects of life.