This post is based on a question that I answered previously on Quora.
As an independent consultant it is generally better to focus on services aligned with your expertise. Otherwise, it will be harder to distinguish yourself in the marketplace.
However, as food for thought if you are going to add a new service, consider offering that service to an existing or past client. You may have a better foot in the door in terms of selling to them as they may at least trust you a bit more than the average consultant coming in cold. While you may have some issues with existing and past customers only seeing you as your “old self”, they may be more willing to take some risk with your new services. Then you can leverage this as a reference case when you approach new clients.