It’s simply not possible to serve anyone that walks through the door. If you try, you’ll wind up neglecting those you can serve well and you’ll be providing marginal service at best to everyone else. You should know the type of individuals and organizations can help and you should actively be screening the people that you can’t. It’s the right thing to do for them and for you.
Ironically, many businesses turn away people just outside of their specialty, but hold the door wide open for anyone inside their niche. They should be doing the opposite. Don’t fall prey to this. Expand the horizons and look for new opportunities to help new people. Simultaneously, put in place the appropriate checks at the door to make sure the right people are getting in. And have the integrity and compassion to politely direct people elsewhere, which means you might want to learn about businesses that are suited to handle their needs, even if you perceive them as competitors.
If you can’t give a customer what they need, you’re asking for trouble by taking their money.