As a kid attending conventions in north Jersey c. 1983 or 1984, I distinctly recall wandering by the TSR tables in the dealer hall at Northeaster 1 or 2, picking up and looking at the $6 RPGA R1-4 modules, not liking the covers, and putting them back down and not buying them.
In the middle '90s, I sold my original run of Strategic Reviews, The Dragons (the oldest issue I had tracked down since starting to read Dragon with #58 was #11), my original OCE boxed set (bought directly from the Dungeon Hobby Shop) and OD&D supplements, and my original Holmes boxed set (a gift from my elementary school gifted teacher and librarian). I hadn't expected to be playing D&D again anymore at the time, and used the money to help pay off credit cards and student loan debt (so at least it was relatively well-spent). Thankfully I kept anything remotely Greyhawk-related, including my AD&D hardbacks and modules, and I've since replaced the other stuff.
Later toward the later '90s I sold my entire MtG collection, which consisted of ~13K cards from Alpha through ~The Dark (with a very heavy emphasis on Unlimited, Arabian Knights, and Antiquties) to a game store in Kansas City, who paid me half in cash and half in store credit. The store promptly went bankrupt within a month, effectively ripping me off to the score of ~$4K.
I live in tornado alley in Wichita, Kansas, so I do worry about the house's roof disappearing during a storm, which would definitely ruin many RPG books up in the attic. Hopefully that never comes to pass....