Mont. Code § 16-6-205
In any prosecution under this code for the sale or keeping for sale or other disposal of alcoholic beverages or the having, keeping, giving, purchasing, or consuming of alcoholic beverages, it is not necessary that any witness testify to the precise description or quantity of the alcoholic beverages sold, disposed of, kept, had, given, purchased, or consumed or the precise consideration, if any, received for the alcoholic beverages. It is also unnecessary to testify to the fact of the sale or other disposal having taken place with the witness's participation or to the witness's own personal or certain knowledge. However, a conviction may be based upon circumstantial evidence reasonably tending to establish the guilt of the accused beyond a reasonable doubt.
§ 16-6-205, MCA