Last week we explained the nature of the prohibition of genebat da'at (see here). We defined genebat da'at as stealing people's minds. genebat da'at takes place when we do or hide something or say something which is not true, with the intention that people will have a good or better impression about us or about an item we want to sell.
Some examples of genebat da'at:
√ A seller should be sincere with a customer. If a woman is trying on a dress and the seller sees that the dress is not a good fit for her, the seller should not tell the woman that the dress looks amazing on her or anything of that sort.
√ Similarly, a seller must tell the buyer the pros and the cons of the product he tries to sell. And if the product has any defect he should not hide it from the buyer. Misleading deliberately a buyer is defined in the Shulchan 'arukh as genebat da'at (choshen mishpat 228:6).
√ The Talmud (Cholin 94a) brings a different category of examples: If I have an unexpected guess at my house and I already had the intention of opening an expensive wine that evening I should not say to my guest: "We are opening this wine in your honor" to make a good impression on him. Or, the Gemara says, if the wine is a simple wine I should not overpraise it to impress my guest and make him feeling that he owes me or he should be extra grateful to me.
√ Similarly, if I know that someone is not going to come to my wedding party because in that particular day he is going to be out of town, and I had not intention to invite him anyways, I should not give him an invitation or tell him: "I wish you could have come to my wedding", to make a good impression on him.