Chullin 94a
חולין צ״ד א — ד"ה וְאִי בָּעֵית אֵימָא
Chullin 94a:5
Discusses forms of geneivat da'at, including presenting oneself or one's actions in a way that causes another to misunderstand what was actually provided. The sugya is a principal Talmudic source for the prohibition, while leaving application to new technologies context-dependent.
וְאִי בָּעֵית אֵימָא, מִשּׁוּם דְּקָא גָנֵיב לֵיהּ לְדַעְתֵּיהּ, דְּאָמַר שְׁמוּאֵל: אָסוּר לִגְנוֹב דַּעַת הַבְרִיּוֹת, וַאֲפִילּוּ דַּעְתּוֹ שֶׁל גּוֹי. תַּנְיָא, הָיָה רַבִּי מֵאִיר אוֹמֵר: אַל יְסַרְהֵב אָדָם לַחֲבֵירוֹ לִסְעוֹד אֶצְלוֹ, וְיוֹדֵעַ בּוֹ שֶׁאֵינוֹ סוֹעֵד, וְלֹא יַרְבֶּה לוֹ בְּתִקְרוֹבֶת, וְיוֹדֵעַ בּוֹ שֶׁאֵינוֹ מְקַבֵּל. וְלֹא יִפְתַּח לוֹ חָבִיּוֹת הַמְּכוּרוֹת לְחֶנְוָנִי, אֶלָּא אִם כֵּן הוֹדִיעוֹ. וְלֹא יֹאמַר לוֹ סוֹךְ שֶׁמֶן מִפַּךְ רֵיקָן. וְאִם בִּשְׁבִיל כְּבוֹדוֹ – מוּתָּר.
And if you wish, say that there is an entirely different reason why one may not send a gentile a cut-up thigh without removing the sciatic nerve: Because he thereby deceives the gentile. The gentile will think that the Jew has exerted himself to cut up the leg and remove the sciatic nerve and that although the Jew could have eaten the meat himself he decided to send it to the gentile. The gentile will therefore be more appreciative of the gift than he would be if he realized that the sciatic nerve had not been removed. This is as Shmuel said: It is prohibited to deceive people, and even to deceive a gentile. § Apropos the prohibition against acting deceitfully, the Gemara cites other statements on this topic. It is taught in a baraita that Rabbi Meir would say: A person may not importune [yesarhev] another to eat with him, making it seem as though he genuinely wants his company, but in reality he entreats him only because he knows that the other will not eat with him, i.e., will not accept the invitation. And similarly, one may not send another person many gifts merely because he knows that the other will not accept them. And one may not open barrels of wine for a guest if they have already been sold to a storekeeper, unless he notifies the guest beforehand that the barrel had been sold. And he may not say to another: Anoint yourself with oil, and place an empty jug before him with the knowledge that he will not attempt to anoint himself. But if he does so for the guest’s honor, to show that he holds his guest in high esteem, rather than to deceive the guest so that he will feel indebted to him, it is permitted.