Of course. I've been doing it since 2007.
I don't do Crossfit, and I don't do large group training of any kind. I do mostly semi-private training (groups of 2-4) with a little bit of 1 on 1. I charge for semi-private what most trainers in my area charge for privates. Do I make as much as a big Crossfit box with 200+ members? Probably not. But I do much better than pay the bills. The downside to what I do is that it excludes most of the population. The crossfits in my area are between $85-150ish a month. I'm average around $400-600/month.