I contacted the broker who represented me in three home purchases/sales and posed the question to her. Here is what she forwarded me. See middle of article.
No Grey Area When it Comes to Real Estate License Issues | Litigators & Counselors Since 1967
She agreed with Elke and said she had only been involved with a transaction that had a finders fee twice in almost 22 years as a broker and both were written documents and involved approval from an attorney for the agency that she was working for. She did not recall the amount and as for the "customary" question, in her experience it is too rare to have a range on Long Island where she is a broker. She further explained that in health insurance for example there are figures for "usual and customary" because every doctor, hospital, etc. negotiates them. In the case of finders fees, they are not the norm, so therefore there is no usual/customary. Once again, this is her experience.