Keltham borrows the coin at 0% interest! That's the kind of trusting relationship they have!
It looks like the other 600 instances of this coin that he owns, with a picture of Abrogail's face on one side, and on the other side 'Sworn by Hell to be pure.' At some point he needs to ask what Hell is swearing Abrogail to be pure about, but that's not important right now.
On close examination, a coin does look sufficiently physically symmetrical, with enough lingering asymmetry for identification purposes, to serve as a randomness source if spun.
"Okay, so this coin can land 'Abrogail' or 'Text'. Now... no, actually, first. I want you all to rescale your old lunch duck numbers to a 1-12 scale where 1 is super unlikely and 12 is super likely, so we're all on the same page about what the scale meant. If you were picking a lunch duck number that meant something totally else, scale it instead. Raise your hands when you've done that, then let's say our commonly-scaled numbers once we've raised our hands."
"Oh, and don't update your estimate off what other people thought, this is just supposed to be your original estimate, but we're making sure all estimates are on the same scale."