Rambam, Mishneh Torah, Laws of Sales, 18:1
2 ב
אָסוּר לְרַמּוֹת אֶת בְּנֵי אָדָם בְּמֶקָּח וּמִמְכָּר, אוֹ לִגְנֹב אֶת דַּעְתָּם; וְאֶחָד גּוֹיִים וְאֶחָד יִשְׂרָאֵל..
It is forbidden to cheat people in buying or selling or to deceive them, whether they are Jewish or gentile [Translation Equal Exchange]
3 ג

Suggested Discussion Questions:

1. What are the limits of this ruling? Is it ever permissible to try and make your product look better? To withold information about it?

2. If we had full knowledge about the things we buy, how would it effect us?

4 ד
Time Period: Medieval (Geonim through the 16th Century)