Sforno on Leviticus 25:14/ספורנו על ויקרא כ״ה:י״ד

1וכי תמכרו, in any sale it is forbidden to disadvantage the seller or the purchaser. For instance, the seller must not skim off any dust particles from the top of the drawer to create the impression that the purchaser receives completely refined merchandise none of which turns out to be substandard or useless. (Baba Metzia 60)

2או קנה, when the purchaser is unaware of the true worth of the merchandise, even if by then it had already come into his possession and he had an opportunity to show it to a friend who is more knowledgeable.

3אל תונו, even though the sages said that there is no overcharging when land is involved. (Baba Metzia 56), this applies to the price charged for the land itself. When it comes to calculating the remaining number of years before the next Jubilee year one must not mislead the purchaser [such as saying that there are 18 years left before the next Jubilee year, withholding the information that for at least 2 of those years the land may not be worked so that the purchaser should pay only for 16 anticipated harvests instead of 18. Ed.]