I always kind of considered that I'd know I "hit it big" when someone in Hong Kong decides to bootleg one of my illustrations (◡‿◡✿)
It's super small scale (only $4USD, that's a pretty great price!), and only one person bought so far, so it's not exactly worth writing home about, but I still thought it was pretty funny.
To be honest, this doesn't really bother me-- after doing my senior project on fanartists, I've honestly started to think it's kind of weird when fanartists (like me) who make money off another's IP get really furious when someone else infringes on their work. Not that these are really the same thing, though. I did report the listing though (but not as IP holder, I think that'd be kinda hypocritical), so we'll see if it gets taken down.
But yeah! Even if it's only a tiny listing, I was surprised. I'd like to say something like "I'm flattered someone thought people would buy this and took the trouble to list it" but I'm sure it's pretty routine for them.
Of course, if this is the kind of thing that bothers you, I would suggest searching for your works on Google Image Search and seeing if there are eBay listings you didn't authorize. The more you know!