People that get tips should make at least minimum wage like everyone else. The employer should not get to pay less because someone gets a tip.

I always try to tip in cash. First so the person getting the tip can decide if they want to declare it as income. Second so it goes where I intend it to go.

20% is a good tip. More is not necessary.

I always decline tipping on the screens.

Never pre-tip. Tipping should always happen after service. You won't get a refund on that tip if the service is bad.

Edit: A word