Simply put, it’s a business agreement, better if in writing (email works.) For some reason contracts between club musicians are customarily verbal only. This is a shame -- contracts, of course, protect both parties’ business interests, and make sure everybody does their jobs. As the bands usually have the most to lose and the clubs the most to gain, they’re rare, even if they are a good idea. Fair Trade Music encourages the use of simple contracts, and, as it happens, the American Federation of Musicians provides free legal contract enforcement for contracts filed by its members.