Draw me some money.
I enjoy drawing. I keep a sketchbook and illustrate most greeting cards I send with a little doodle or two. I even go so far as to keep a miniature set of watercolors with me when I travel. This doesn't make me special or anything, in fact, many of my friends draw regularly in sketchbooks or journals. And, like most of my drawing pals, at one point or another I wasted money on an expensive technical drawing set.
A set like the Koh-I-Noor Rapidograph seen above is purchased or received as a gift with visions of all the amazing illustrations that will magically flow from it. One or two pens actually get filled with ink. Within a few days they get clogged. The pens are inevitably put in a drawer or closet and forgotten. Eventually this virtually unused art supply set is donated to a thrift store or sold at a garage sale or given to a friend and the cycle continues.
So, basically, what we have here is an art supply (a genre of consumer items notorious for being over-priced and bought on impulse) that is frequently seen on the second hand market in excellent condition. Most folks reselling these items locally just aren't aware of the ridiculous costs of these things. The suggested retail (list) price of this set of 7 pens new is over $150!!!
These pens are very high maintenance, and clog easily, so they just aren't practical for most casual creative types. Because they are often sold (and resold) in sets, usually 4 or 5 of the 7 pens are 100% unused. And those clogged ones can be cleaned. Check the recent completed eBay listings: As of the time of this posting, we're looking at $20-$50 dollars for a decent used set, easy!
I find these things all the time, usually for well under $10. If you live near an art college, I even recommend doing a little dumpster trolling when the school year ends. Twice I've seen a Rapidograph set in great shape, complete with packaging, in the garbage.
Technical pens are a great example of an item that has great value differences in regards to context. They are pretty common and inexpensive to pick used locally, and then sell very well for decent dollars on the online reuse marketplace. The demand for these high-end art supplies is much higher when offered to the global world of potential buyers online, whereas your local thrift store might be hard up to find someone who casually will drop big bucks on some old drawing pens.
Here are a few more pictures of technical drawing pen sets that I've resold for decent cash from other brands like Mars Staedtler and Reform:
UPDATE: I've recently had an auction of a complete set of Rapidographs go horribly awry when the ink exploded during shipment. I was lucky that the buyer was understanding and only wanted a partial refund. So, either wrap that ink up really airtight in a separate baggie or maybe don't even include it in your action at all.