Sforno on Leviticus 25:17/ספורנו על ויקרא כ״ה:י״ז

1ולא תונו, the reason this is repeated so many times is to warn you that you must not even misrepresent by words and thereby treat your customer unfairly. Even if the damage caused is not measurable in terms of money, all manner of misrepresentation is forbidden.

2כי אני ה' אלוקיכם, I, G’d am both buyer and seller. This is why I am meticulous and adamant that neither practice be tolerated.