Provisions in contracts can vary depending on customs within different areas of the country, how established the artists is, supply and demand and numerous other factors.
When I first started using contracts I met with reluctance...but as time went on and employers realized it was really an agreement as to what is expected of both parties, they liked the idea of a contract.
In the majority of cases I supply the contract. When I work under the employer's contract I often have to add a provision or two, just to keep things on an equal par and fair.
Realistically, most of my bookings are made anywhere from 3 months to two years in advance. Consequently I give them the opportunity to opt out, at half the fee, between date of signing and 90 days prior to the job...with the exception of New Years Eve, which is non-cancellable from the get go.
If cancelled during the 90 days prior to the job, they are responsible for 100% of the fee. In the last ten years, I have only had to enforce that once...and that was because the venue changed the date without telling me. They balked, but settled without litigation.
In the interest of fairness I have made an occasional exception. A kitchen fire forced the closing of one club during the time I was to play there. I did not hold them to the contract in that instance.
Regarding liability to patrons: One club I work has a stage that sits 3 1/2 feet above the dance floor with removable steps to access the stage. Patrons have often tried to get on stage to make requests, announce birthdays, etc. and found getting on and off stage treacherous. One such patron tripped on a mic wire once, and I had to put a clause in the contract saying I could not be held responsible for anyone on stage but myself.
Eddie