Small thing but "chotto muzukashii kana" isnt really a flat no. That kana at the end softens it a lot, almost like shes thinking out loud, so it lands more like "hmm that might be a bit tough" than a hard pass. In a work setting shes basically saying no without putting it on you, since turning something down straight can come off cold between coworkers. The bigger trap is that this exact phrasing gets used for everything from "I really dont want to" to "sure but its a hassle," so you cant always read it the same way. It helps to watch what happens after, like if she suggests another place or just goes quiet.

Applies to everything, more is never better.

Wait, does yours actually say "CIA" on the stamp, or is it just that generic note about the Brussels fair? I've seen that printed blurb in a bunch of paperback editions, so I'm curious if yours has a real agency marking or if it's just the publisher's little history lesson.