What qualifies as a professional fee?

Good day, could you please elaborate on what exactly constitutes a professional fee in the realm of cryptocurrency and finance? Are these fees associated with the services rendered by experts such as financial advisors, tax consultants, or cryptocurrency traders? Furthermore, are there any specific criteria or standards that need to be met for a fee to be considered professional in nature? Lastly, how do these fees typically compare to other types of expenses in the industry, and what are some common pitfalls to avoid when it comes to professional fees?