In your time staying at the bar you've consistantly heard hunters discussing the wonders of salt on incorporeal undead.
From overheard whispers and jokes it seems that a handful of salt thrown at a ghost will make it dissapate, making it unable to do anything in the physical world for some time.
You have heard a rumor that one hunter was able to figure out a man was a shapeshifter by shining a bright light into his eyes. Something about it revealed that he wasn't the man he was pretending to be.