One may not deceive or trick others when it comes to monetary transactions.
If one knows that one’s merchandise is flawed or faulty, one must reveal this to the buyer. For instance, if one wishes to sell his home and he knows that the ceiling is full of mold because of a burst pipe but this is completely unnoticeable as the ceiling was recently painted, the homeowner must relay this information to the potential buyer. Although it would seem that withholding this information is not an outright transgression of stealing, for the buyer is erring on his own and the seller has not extorted money out of the buyer through trickery, this nevertheless constitutes the prohibitions of fraud and deception and is absolutely forbidden.
Similarly, if one wishes to sell his car and he knows that the car was involved in a serious accident which caused significant damage to the body of the car but the buyer knows nothing of this because he relies on the seller and trusts him completely, the owner of the vehicle must certainly bring such a defect to the buyers attention. Nevertheless, there are minor flaws which the seller need not bring to the attention of the buyer and in such situations, a prominent Torah scholar fluent in the monetary laws of Shulchan Aruch must be consulted.
This sometimes creates a great pitfall, for people do not always realize the severity of this prohibition. This is especially true regarding people selling cars and conceal various mechanical and body issues for the sale to go through with ease. This is absolutely forbidden, as we have discussed.
Just as it is forbidden to deceive and trick a fellow Jew, it is likewise forbidden to deceive non-Jews.
Deceit Regarding Other Non-Financial Matters
Besides for the prohibition of deceit when it comes to monetary transactions, it is likewise forbidden to deceive others even regarding issues completely unrelated to money. It is therefore forbidden to trick another into believing that one is doing something for him when this is indeed not the case, for instance, if one implores his friend endlessly to eat with him and the individual inviting knows that the invitee will not sit to eat with him (because he is in a rush and the like) and he nevertheless continues pleading with him to do so in order to make it seem that he really wishes to honor his friend, this is considered a form of deceit and is forbidden. Many erroneously believe such things are permissible as a result of a lack of awareness of Halacha.
The Sefer Meirat Enayim (a commentary on the Choshen Mishpat section of Shulchan Aruch authored by Hagaon Rabbeinu Yosha Volk Katz who also authored the “Perisha” and “Derisha” commentaries on all four sections of Shulchan Aruch) writes that nevertheless, if one invites his friend to sit and eat without pleading and merely in a polite manner as is customary, even if one knows that the individual will not sit and eat, there is nothing wrong with this, for if one does not extend an invitation to sit and eat at all, it will be considered disrespectful.