asking for a refund after the session seems to be bad form. if I stay the entire session, I always tip, even if the session is not what I expected.
On one occasion I walked out while in a country not too far from the land of smiles. I was a walk in to the place and… S/he wasn’t what i expected ‘her’to be, and when we both realized it was an honest mistake, I politely exited with a refund, but I did slip my attendant a small tip for ‘her’ time. Another time I went in blind to who I would be assigned as my attendant, when she walked into the room I looked up to greet her and she had a very large and open ‘cold sore’ on her lip. My opinion was she should not be working and left with the house fee. And… one other example, in india my attendant walked in and he was probably 7 feet tall and had hands the size of the giant he was. I had asked for a female when I went in and as often happens in Asia, they thought that once I was face down I wouldn’t notice until it was too late! That was kind of funny at the time.