Mont. Code § 16-6-206
In proving the sale, disposal, gift, or purchase, gratuitous or otherwise, or consumption of an alcoholic beverage, it shall not be necessary in any prosecution to show that any money actually passed or any alcoholic beverage was actually consumed if the court hearing the case is satisfied that a transaction in the nature of a sale, disposal, gift, or purchase actually took place or that any consumption of an alcoholic beverage was about to take place. Proof of consumption or intended consumption of an alcoholic beverage on premises on which such consumption is prohibited by some person not authorized to consume an alcoholic beverage thereon shall be evidence that such alcoholic beverage was sold, given to, or purchased by the person consuming or being about to consume or carrying away the same, as against the occupant of the premises.
§ 16-6-206, MCA