21 CFR §1314.25

1. (a)Each regulated seller must ensure that sales of a scheduled listed chemical product at retail are made in accordance with this section and § 1314.20.
2. (b)The regulated seller must place the product so that customers do not have direct access to the product before the sale is made (in this paragraph referred to as “behind-the-counter” placement). For purposes of this paragraph, a behind-the-counter placement of a product includes circumstances in which the product is stored in a locked cabinet that is located in an area of the facility where customers do have direct access. Mobile retail vendors must place the product in a locked cabinet.
3. (c)The regulated seller must deliver the product directly into the custody of the purchaser.