I can't say "l never have, nor ever will". I saw a regular last year, and the service (normally extremely good) was, on this occasion, wonderful. As l am a regular, it's a 'pay on exit' arrangement.
I gave her an extra £10, as a tip to thank her for the heightened service.
Since then, she continues with the increased levels of satisfaction, and l have never tipped above the standard price since.