When you meet with clients, you need to be absolutely clear about the services you will provide—and those you will not. You should be firm in your intent to follow liquor laws; refuse service to underage guests; limit service to guests who drink too much. Your contract agreement should be specific about hours and services and include a release from liability for incidents related to alcohol served at the party. The host should supply the beer, wine, and alcohol for the bar, and there should not be a charge to guests for service; state and local laws may require a license if you are involved in the resale of alcohol. (Consult your state alcohol licensing agency or a civil attorney for details about necessary permits or licenses if you want to get involved in resale.)
Your agreement should also specify the supplies you’ll need for the party: glasses, utensils, ice buckets, ice, sodas and mixers, napkins, and cleanup necessities. You may want to work with a party supply company to rent glassware; make certain that responsibility for any breakage passes through you to the host. Your role may be limited to working at the bar, or you may be asked to be a member of a setup or cleanup crew.
When you being a freelance bartender, you have to determine the host’s expectations for your attire; should you wear your brightest Hawaiian shirt, or rent a tuxedo? During the party, remember that you are working; you are not a guest. Don’t sample the alcohol at the bar, and keep your involvement with guests on a professional level.