This is an interesting topic but I think 'etiquette' would be a better choice of words than 'code of ethics'. I have a couple of stories in that regard.
Once I was with an SP, and after she had taken her clothes off it appeared that she had not shaven her legs and prepared properly. She said this would be a true GFE experience since she was not truly diligent in that regard. I just said "wow, its too bad I shaved my balls else I would be able to provide you with a BFE experience!"
The other issue is that of the donation. I usually place it in a plain envelope in plain view (on the coffee table or whatever works) and never discuss it or mention it at all. SPs usually discretely take it away at the end of the session. Even if they want to count it at the beginning, I expect her to excuse herself to the bathroom and take care of it there. Well with one SP I saw she came in, asked in a loud voice "is that the money?". I said "yes", and then she said "So for 2 hours it should be $320", then opened the envelope in front of me and started counting.