easy … just pay the actual cost to her and just dont give the tip… if they give you “that” look , which warms your heart and forces you to give them the tip , remember , this is nothing but a form of bribery …
We people who work in offices , we believe if we get the job done properly and keep the client happy , they will use our services again …
that is the same concept behind every business, if you like the way she has done your eyebrows, she got the gift from you , in the form of you becoming a regular customer for her…