Sometimes when I wonder if my players being able to get valuable old manuscripts, tomes or artifacts out of dodgy auctions or similar is entirely plausible, something like this happens. Here is a 3.2 million dollar piece of artwork, which was found stolen over 10 years ago suddenly turning up in the mail and being seized again (for its rightful owners this time). Just goes to show that no matter how valuable or precious something is, someone is probably going to try to steal it and then manage to send it places in the post. At least until they made some kind of mistake and got caught out anyway.
In any event, the next time I need to point out that valuable stuff like artwork does gets stolen and shipped around for who knows what purposes, this is a nice little incident to keep in mind.