It creates a stupid situation anyway, what if it’s busy and you pay extra to eat in, but then can’t find a table so leave anyway? Crepe Affaire still does charge an additional £1 per item to eat in, which is ridiculous.
You can save money therefore, by always saying you’re going to takeout, even if you plan to stay and eat in. Your coffee may come in a paper cup instead of a china mug and you may have to eat with a plastic fork instead of a metal one. Your McDonald’s will come in a bag instead of on a tray. If you feel like you’re ‘breaking the rules’ somehow, just sit far enough away from the counter that the staff can’t see you, they won’t care anyway they’re too busy with the next customer.
The only time you should ever pay the extra for eating in is if you are in a small independent shop staffed by the owners. But if they charged you extra to eat in, don’t feel obliged to leave any tip.