Client backs out last minute!

I applied for a project for web maintenance off of Craigslist and the company 'hired' me and the projected start date was tomorrow. Well, I get an email today stating that they found someone in-house to handle the updates. I am so frustrated b/c this was a good chunk of money, which they decided upon, and we have been talking for a month now about the details of the contract. So it's just like time wasted.

I'm just wondering, how often does this happen to others?

Nothing is final until it's signed, sealed and delivered. Sorry for your loss

As Julian said, its not final till its signed. Just move on from this as a wiser person.