First, why does it matter if you wrong your fellow in real estate transactions? Why not simply care about one's bottom line? From a practical standpoint, markets would either not last too long or they would be on shaky ground if there is no credibility. Being able to trust other actors in a given market is what makes an economy grow.
Since G-d is not one to be superfluous in repeating the same admonishment twice, it would help to explain the difference between the admonishment in Leviticus 25:14 and Leviticus 25:17. In the first mentioning, it refers specifically to overcharging or underpaying in property transaction (Bava Metzia 50b). In the second mentioning, it refers to deceptive speech (Midrash, Leviticus Rabbah 33:1). In the specific context of business, one cannot verbally deceive the merchant with false hope of buying something when there is no intention to buy (Bava Metzia 58b). It is also forbidden for the merchant to deceive the customer with false advertising or misleading the customer into thinking they are purchasing something that they in fact are not (Choshen Mishpat 227-228). In the passage, there is also the phrase in Leviticus 25:17 of ויראת מאלהיך כי אני הי (fear your G-d because I am the L-rd your G-d). This phrase shows that business ethics are an intersection between humankind and G-d. Even though G-d was not directly involved in the financial transaction, He still gave this as a divine decree because people are created in His Image and should be respected for that reason, which is why the halacha behind business ethics applies to both Jew and non-Jew alike. In a general context, Rashi extends the admonishment in Leviticus 25:17 beyond the business realm and to harmful speech in general (Rashi's commentary to Leviticus 25:17).
Going back a few Torah portions, we see the phrase אני הי (I am G-d) repeated often enough in Leviticus 19 to make the point that we act in a holy manner because these laws come from G-d. However, I have to wonder why G-d felt He needed to mention אני הי only in Leviticus 25:17, and not in Leviticus 25:14. Why does G-d need to remind us of Him when it comes to verbal deception and not monetary deception?
I would argue that G-d needs to give us the extra reminder because it's easier to commit verbal deception. A court of law can prove fraud or embezzlement, but it cannot prove one's intent behind one's words. Only the individual and G-d can truly know one's intent, which is something that can be easier to hide than monetary deception. Monetary transactions tend to have transparency. Words, on the other hand, can be a tricky business. Words can be massaged to deceive another individual, even when they are technically true. Words can even be maliciously used when the target of said words does not even know about it, which is why the Jerusalem Talmud (Peah 1:1) likens foul words to an arrow because of the damage it can do from a distance. When you cheat an individual with words, you steal more than money. You steal their dignity because you make them look foolish. At least with money, the individual can be caught and the damage can be undone, but when you wrong someone with words, the damage is not so easily reversible (Choshen Mishpat 228:1).
As Hillel mentions in Pirke Avot (1:14), "If I am only for myself, what am I?," and does so to remind us that in this specific context, business transactions are about more than making profit. We have a responsibility to others when conducting business. We also have a responsibility to use our words to treat others with dignity, regardless of whether they are spoken during business hours. By stating twice that it is wrong to aggrieve another, G-d was expanding that both to physical and verbal transactions. Although this Torah passage deals with property transactions, the moral here is that we should be constantly concerned about the wellbeing of others and that the measure of our conduct towards others is a solid metric of our own holiness and connection with G-d.