Ha, I narrowly avoided exactly this situation. Had an offer signed, then got jerked around in the background check process for a few weeks, and then finally got a "sorry, we found a more qualified candidate, so we're rescinding the offer".

Must say I was glad that I grit my teeth and refused to put in my notice at my other job. The schadenfreude and relief at having dodged a massive bullet really kicked in when I found out who was the "more qualified candidate" eight months down the line at a local DevOps days.