What is a good commission fee?

I'm curious, what exactly constitutes a good commission fee in the world of cryptocurrency and finance? Is there a standard percentage that is widely accepted, or does it vary greatly depending on the type of transaction or the platform being used? As a professional practitioner in this field, I'm interested in understanding the factors that go into determining a fair and reasonable fee, and how to ensure that I'm getting the best deal possible without compromising on the quality of service.