You know the little acidic twinge you get in your gut when you read a Gawker post about the latest underqualified-seeming asshole who just sold her first book for six figures? What if I told you that you never need to feel that way again?
The answer is a little purple pill called Nexium. No, j/k. The answer is understanding that accepting a six figure deal is one of the biggest career mistakes a first time author can make.
Don't get me wrong, writer types: publishers want your book to do well, badly. They just really could not give a fuck whether you do well ever again. And that's why they're willing to gamble on your novel/memoir being an enormous breakout success to the tune of several hundred thousand bucks. If they're right, it's a win/win. But on the (overwhelmingly likely) chance that they're wrong, you're mega-fucked, and they're on to the next next big thing.
When people read the phrase 'six figure advance,' they usually pretty much stop reading after the first two words. But the word 'advance' means that your book has to sell enough copies to make your publisher that much money, plus production costs, plus more, or else it's a flop. Let's say you take a big advance for two books. Your publisher will try to justify its cash outlay by printing a bunch of copies, and unless you win the logicless lottery of book success, most of them will be returned by the bookstores. So you'll come nowhere close to earning out your advance with the first book, and your publisher, discouraged, will barely publicize/ print any copies of the second book, crippling your chances to recover from the failure of the first one. Now your 'sales track,' which is the only thing other publishers will thoroughly consider when your next book is out on submission, is ruined. The only thing left to do then is try to convince another publisher that all your failures up until this point have been the fault of your previous publisher. This will be the truth. Unfortunately, it will probably garner the same unenthusiastic response that the truth usually receives.
If you're wondering why your agent would fail to protect you from this unfortunate outcome, it's because she heard "six figure advance" and then dollar signs replaced her pupils, her tongue stuck out like the drawer of a cash register and there was a ca-ching! sound effect. No one wants 15% of nothing much, after all. However, nothing much might just be what's best for your future.
Unsolicited is written by an editor who prefers to stay anonymous in the (probably misguided) hopes of remaining one.