That's what a six-figure-a-book ghostwriter told me. He was worried that he would have to ditch the much less lucrative history-book writing. No need for that, I told him. Just rebrand your ghostwriting identity. He did. He created a "pen name" for ghostwriting.
Recently I had my own challenge in my hybrid identity as both a syndicated blogger for three sites and as a ghostwriter. One prospect couldn't understand that I could simulate his voice, despite the strong voice I use to blog. I didn't get the assignment.
My solution has been to keep the blogging under wraps when pitching myself as a ghostwriter. The exception is if the assignment is to ghostwrite blogs which demand a lot of traffic. My track record along those lines for my own blogs provides evidence that I can accomplish that.
In short, we ghostwriters have to be selective in which of our brand identities we present when competing for assignments. Once we learn that lesson, we get more work with less explaining to do about our multiple sources of income. Most users of our services get confused by multiple brands. So, just present one to them.