I used to work as a chef in a fairly upscale restaurant where I live. This is in the Us so it's probably different than Europe or the UK. The wait staff here work for significantly less than minimum wage, and do rely on gratuity 'for a job well done'. While it was the restaurants policy that the staff kept any cash tip's they recieved, any thing on a card was both charged a processing fee, and paid in their weekly check so they paid tax on the gross amount. I'm now in the habit of leaving a cash tip for a job well done.