I had a great experience a couple weeks ago with my injector Shruti she was super hands-on and spent her time with me, I felt really comfortable. My dysport looks amazing my forehead is flawless.
I have been getting Botox now for a few years but never have I been asked to tip the injector as I'm checking out.
My only suggestion would be instead of asking if the client would like to tip vocally at the end of the service have something on the card machine asking to leave a tip rather than putting the person on the spot super awkward LOL but overall I had a good experience and will be back.