So I'm working on a novel that I hope will sell bunches but if it doesn't, I'm trying to think of other ways to make money through writing and I happen to have an idea for a humor/how-to book involving a celebrity that I'd like to ghostwrite, of course. This celebrity has a literary agent -- her memoir came out not too long ago -- should I pitch the idea to the literary agent? Or her manager? And if the agent doesn't take unsolicited queries, is that an end for me? Or can I get around that, as this is about another client of his?
I guarantee you the celebrity does not have a literary agent. I guarantee you that her ghostwriter does. You need the celebrity to sign on before anything else so you have to talk with the manager. This will be an INCREDIBLY hard sell if you don't have a track record and you just come a cold calling.
You'd do well to keep working your way down the list of ideas before investing too much in this one.