Is it permitted to buy jewelry during the Nine Days? If not, is it permitted to sell or is it lifnei iver?
One should not buy jewelry in the Nine Days, because it is a type of purchase that brings the buyer joy, and one recites the blessing of “shehechianu” upon buying it. However, it is permitted to sell jewelry even in the Nine Days.
Sources: Concerning buying jewelry, Iggros Moshe (Even Ha’ezer, IV, no. 84) prohibits the purchase of jewelry for a bride, because it is a part of the joy of the wedding. Buying jewelry without connection to a forthcoming wedding would not be included in the Talmudic prohibition, but is included in the general instruction to limit one’s dealings, in particular those that cause joy (see Mishnah Berurah 551:11). However, because this is not a full prohibition, the laws of lifnei iver and mesayeia (lifnei iver is usually inapliccable because there are alternative stores to shop at) would not apply. This is also the ruling given by Chazon Ovadya, Fasts, p. 168.