Hmmm, why Should the restaurant charge you a mandatory 18% tip without prior notice? That's unfair if you ask me at least if u had the info, you will conveniently take your decision. Tips shouldn't be mandatory but a voluntary action if I am pleased with the service received and if I really have enough with me to tip.
Really some people are just too good with their job that after their service, I am moved to tip them but let no one force me!