Typically, an agency will charge its escorts either a flat fee for each client connection or a percentage of the prearranged rate. In San Francisco, it is usual for typical heterosexual-market agencies to negotiate for as little as $100 up to a full 50% of a woman's reported earnings (not counting any gratuity received). Most transactions occur in cash, and optional tipping of escorts by clients in most major U.S. cities is customary but not compulsory. Credit card processing offered by larger scale agencies is often available for a service charge.