After a number of books published,I've recently been offered a new contract. The one proviso is that I use a pseudonym. Of course everyone is being nice about it and calling it a 're-launch', but it's pretty obvious it's because my previous sales haven't exactly been stellar. I'm a bit worried that if the publisher doesn't really get behind this book that I'll end up writing under hundreds of different names. What do you think about this pseudonym business? Pros? Cons?
It's difficult to answer this question fully without knowing what sort of book it is, who the publisher is and exactly what sort of publishing history you've had. It's quite unusual for a publisher to suggest that an author change their name after they've already been published a few times. Clearly, they think you're a very good writer because they want to still publish you; the fact that they want to do it under another name is somewhat perplexing, as it means they'll be launching new-you as a new writer, and launching a new writer can be a challenge. If I were you I'd be asking them why they feel they're going to have better luck with you using a new name and what plans they have to ensure the 're-launch' works. One would certainly hope they'd be getting behind this new book if they're going to the trouble of launching new-you.
It's unlikely you'll end up writing under many different names - unless you want to. There's certainly a sort of career to be had in ghost writing or co-writing, and some writers don't want to use their real name for this as they'd rather save it for work that's just theirs alone. So the pros of a pseudonym include the fact that you can merrily publish some material that you don't want to put your name to for various reasons; one of the cons is that you're always going to wonder why you couldn't make it under your own name.
Fundamentally, go with your gut instinct: if you feel uneasy about using another name, trust that feeling and talk honestly with your publisher. It's your writing, after all, and no one can force you to do anything. Of course, it may mean that you don't get published with this book, but maybe another publisher will want to publish you and get behind you with your own name.