The Eighteenth Amendment was the result of decades of effort by the temperance movement in the United States and at the time was generally considered a progressive amendment.
In a sales contract, the parties are the seller(s) and buyer(s) of the real estate, who are often called the principals to distinguish them from real estate agents, who are effectively their intermediaries and representatives in negotiation of the price.
A Buyer's Agent has a written agreement with the buyer that spells out the terms of how the agent will get paid. You need to read and understand your agreement to determine how your agent will be paid.