I'd actually approach them rather like you did the issue here in the journal. Tell them you're a regular customer and point out the reasons why you're a regular customer, and then instead of making the smoking issue be about the law, point out the other reasons why you dislike it -- after all, it's not that you're irritated with the shop because they're doing something illegal, but because you would prefer to patronize a non-smoking place, and if they followed the law then they would be such a place. I'm positive you're not the only one who feels this way about their coffee/tea shops, and so you may not be the only one who has said something, and the more people who say something, the better.