If it goes against my morals/integrity/etc, probably not. As others have alluded to, it's pretty hard to picture this scenario without specifics. That being the case, every scenario I can think of involves the harm of someone else (whether physically or mentally/socially); and that is something I would never do for any amount of money.

Now, if someone asked me to sell out in my writing career for a few million, I would do that in a hear beat probably. I would write the crappiest, cringe-inducingest thing if I was getting a bunch of money for it. Preferably, this would be under a pseudonym of mine. Regardless of if that were the case, I would be vocal and go public about the deal made with full disclosure that I think it's crap.