I know the objective is to make money, but wouldn’t you rather have a smooth experience while making your money?
When you get an inquiry for your services, you can tell a bit about your potential client by the way they interact with you. The way they address you to the way they inquire about their needs can help you determine whether they may be a troublesome client. Is your potential client on top of things when you ask them to provide you with specific details? Do they wait for days to reply to you? Are they formal in their speech? All these things should be considered when you are considering a potential client.
Finally, your gut–in my case the Holy Spirit, always lets you know when something may not be such a good idea. Listen to that voice/feeling, and make your decisions along with all of the physical inklings you’ve received. All money isn’t good money. Your peace of mind is invaluable.