by Jennifer Crusie
While the main characters do refer to their budding relationship as "The Cinderella Deal", Crusie manages to make the plot vastly different from that of the historically famous waif rescued by magic and a prince.
Instead, she's got sassy, energetic Daisy and, seemingly, lifeless Linc. He's a college professor with no time for his neighbor's silliness. She's an artistic sort who has never learned that a little order can make life sweeter. The two are at odds early.
Linc uncharacteristically lies himself into a corner, and realizes that the only way out is to convince his flighty acquaintance to be his fake fiance. Soon enough, the lie grows until it seems there is little chance of escape.
I read this months ago. It was fun, but I don't remember why. Sorry.