Avodah Zarah 14 - Devotion to Idols
The following items may not be sold to an idolater throughout the year: fruit of specific cedar trees with their stems, pure frankincense, and a white rooster. Since idol worship is included in the seven Noahide laws, a Jews selling these items - which were used for idol worship back then - would be "putting a stumbling block in front of a blind man."
However, selling a large bundle of these items is allowed. It can be assumed that the buyer is a merchant, who will be reselling them at a profit, and the "stumbling block" prohibition does not go that far.
If an idol worshipper asks for other items, specifying that they are for idol worship, it is prohibited to sell them to him. One cannot rationalize that this man is simply so devoted to idol worship that he expects all others to be as devoted and sell to him at a discount.
The tractate Avodah Zarah of our father Abraham was comprised of 400 chapters. We have only five, and we encounter difficulties even with these, since we are not certain which cedar trees are meant above.
Art: William Trost Richards - Cedars on the Shore Near Atlantic City