When I edit for individual authors, I typically get thanked in the acknowledgments section, and I can list it on my website. Not so for agency work.
Most of my non-fiction work comes through specialized editing companies that handle the advertising, client communication, payment collection, and so on. This comes with two costs: (1) the difference between my typical rate and the agency’s pay rate (this is not a commission, as each agency negotiates its own rates with their editors and their customers) and (2) the non-disclosure agreement.
The author is the agency’s customer, not mine. All agencies require that I not try to poach their customers. (Fair enough!) Most also require that I not reveal which manuscripts I’ve worked on. This is a little trickier. For writing work, there are different rules in different places — “work for hire” in the US vs. “moral rights” in Europe, for example — but editing something doesn’t make one its author.
Whether to give up an effective advertising tool (look at this great thing I worked on!) and make less money per word / per hour should depend on what is gained in return. I’ve fired two agencies because their extra paperwork makes their pay rates too low to be competitive. Other agencies haven’t hired me because my pay rates are too high for them to make enough money.
It’s a balancing act. To edit as a professional means turning down some work because it doesn’t pay well, taking enough work that you can show, but still getting enough work to survive while you build a client list.