Parshat Behar mentions the prohibition of taking too much profit (אונאת ממון). The laws of Shemitta (the seventh year) are designed to remind all Jews that their land is a gift from Hashem. The laws of overcharging are tied in with the laws of Shemitta because it also shows us that all of our possessions are a gift from Hashem and if we abuse these gifts or use them selfishly, we do not deserve to keep them.
The Isur of אונאת ממון is deeper than one might think. Just as the vendor cannot deceive the buyer of an object's value, there is also the prohibition of אונאת דברים, offending someone verbally. One cannot make the impression that he will buy an object when he has no intention of doing so. When someone sees another person suffering, he cannot say the person deserves to suffer because of his sins. Answering a question rudely or purposely giving an incorrect or misleading answer is also as example of אונאת דברים. When dealing with אונאת דברים the Parsha says, ויראת מאלקיך - "And you shall fear your God." This phrase comes to teach us that אונאת דברים is very stringent. Because money could be returned but hurt feeling cannot be healed, we learn that דברים אונאת is a graver sin than אונאת ממון (see Baba Metzia 85b).
The Torah concludes its discussion of Ona'at Mammon by stating ויראת מאלקיך - and you shall fear your God. Rashi explains that sometimes it is not clear if one is truly violating this law and only Hashem knows if one is violating this law. The Torah emphasizes that we must bear in mind that Hashem is watching us at all times and He will ultimately judge us and hold us accountable for our misdeeds.