You will want to find a headshot photographer who specializes in acting headshots, not a photographer who can also do headshots. Look at their portfolio. Do they continuously show the same examples, or do they have a strong body of work with consistently high quality specific to actor’s headshots?
The technical aspects and composition of the photography is only a small part of being a headshot photographer. More effort should be focused on the actual “acting” or what you bring to the headshot as far as your expressions.
As an actor myself, I know the ins and outs of the industry and what casting agents are seeking in headshots, and I know how to draw that out of you. I also spend a lot of time working on your specific look and expressions that will best show you off to agents and casting directors.