It says gullible on the ceiling

Hark! "Credulous" hath been inscribed upon thine rafters!

But if you were gullible, you wouldn't bother to check. You'd just take the word of the person at face value.

If you have a sharpie and a bartender that isn't paying attention, writing "gullible" on the ceiling of a bar once can net a lot of free drinks over time.

Especially in a place with lots of tourists and not many regulars.