I very,very rarely tip. Twice in 6 years.
Once because I enjoyed the session so much I gave an extra tenner.
Second time is because I already had a substantial discount off the stated price, she traveled through the recent snow to see me. Her car got snowed in, she took a taxi, 2 trains and a final taxi to the apartment, it took her two hours to see me for a 1 hour punt, and I was her only punter that evening. for such dedication and a fucking top fuck too, plus we went substantially over time, well she defo deserved an extra £20. that's the only two times though.