Bartender Pricing (Premium Quality)

Why does one bartender quote $30/hour while another quotes $50? Here are the variables that move the needle:

Most freelance bartenders expect the host to provide the bar infrastructure (tables, tubs for ice, glassware). If you need the bartender to bring a mobile bar station, back bar, or glassware, this is usually an add-on fee ranging from $50 to $200. bartender pricing

This paper analyzes the relationship between price and tipping in the restaurant and bar industry. The author finds that customers tend to tip more as a percentage of the bill when prices are higher, but the effect is non-linear and depends on various factors. Why does one bartender quote $30/hour while another