27 CFR §31.36

Any person who sells or offers for sale distilled spirits, wines, or beer, in quantities of 20 wine gallons (75.7 liters) or more, to the same person at the same time, shall be presumed and held to be a wholesale dealer in liquors or a wholesale dealer in beer, as the case may be, unless the seller shows by satisfactory evidence that the sale, or offer for sale, was made to a person other than a dealer.