Must have been during the first few years of eBay. I wasn't playing D&D at the time. I had a lot of modules and I could use the cash (for bills.)
I sold a bunch on eBay. :(
Once my sales count got up into the teens, I started having sellers remorse and I stopped selling.
I've since bought most of them back, from eBay and Bookmans, and more. :)
I'm still looking for this one at the right price...