I just went to the car wash, and the guy asked me to add a tip. I interacted with him for 5 seconds, and all he did was slide my card. I interacted with a girl that waved me forward and pushed a button.
I'm all for rewarding employees, but there are way too many businesses expecting tips for their employees that previously didn't.
If you want your employees to make more money, charge me more and add it to their paycheck. But don't make your employees awkwardly ask "Would you like to add a tip?" when I've known them for less than 10 seconds.
I'm not against all tipping. In fact my favorite time to tip is when it's not requested or a line item to fill out on a receipt. I just don't like this pattern developing.