I got a PM from a RS type who said they were in a restaurant with a service charge and they were asked for a tip. I didn't ask if literally. My personal rules for Budapest are:
If directly asked, with or without service charge the answer is no. It's happened maybe 3 times in 20 years.
If they hand me the credit card machine and it is set up for me to click a percentage for a tip. With a service charge and VERY good service, they get 5%. Without a service charge and good service they get 10%.
Otherwise I round up to about the same.