How exactly are they bringing up religion? Are they asking to have prayer before a presentation or something?
I do not bring up my atheism with my religious friends. If they have questions about atheism and how I came to be an atheist I will answer them. I became an atheist through my own thoughts and experiences. Nobody else pushed me towards it. That's why I do not like being preachy with my friends. Me telling them why believing in their god is stupid will not cause them to suddenly renounce their faith. It will just cause tension and resentment, which I do not need nor do I want because my friends, no matter what their religious beliefs, are still good people and still have my back no matter what. However, I have no problem telling associates of mine who spew bigotry and ignorance without thought what's what.
I've been "out" for at least a couple of decades. I, too, am in business. I do the absolute best possible job I can for my clients. I've actually had Christians come and seek out my services, not because of my lack of belief, but rather the quality of my work. Yes, you're going to lose some business. But, assuming your not selling religious artifacts, I think in the long run you'll be better off. Working on the theory that you're good at what you do, that will generate business for you more than tambourine banging and arm waving. When it comes to the pocketbook, people are more interested in getting what they pay for than getting the blessings of magic juju spirits. That's what Sunday morning is for.