Mr. B has earned more money writing than I have, in part because he’s good at writing for others. (I’m only good at writing for me — but don’t let that sway you; I’ve turned down loads of copywriting work simply because it doesn’t interest me. If it interests you, know that it’s out there waiting for the right writer. Right?)
I’ve only read a little of Bowerman’s work, but between that, Tom’s recommendation, and that of a dozen other writers I respect, you’d be smart to investigate the Well-Fed Writer if you’re curious about writing commercially.