You can work with clients all over the country. But it does take effort to market your services. You must choose a field of interest, find out who publishes in that field, and send letters to the right person. Once you have clients, they will continue to call you, but it never hurts to make marketing efforts. Each contract is negotiated.
Most people find marketing and negotiating intimidating.
It is a matter of knowing what you have to offer and asking for what you want.