I do a ton of resale. I found a first edition first print last year for $3 at a thrift store, and thought I hit the gold mine... It turned out it was the book club version so it's only worth about $50-$80. Was a huge bummer.
I'm starting to post some of my thrifting and freecycling stuff again after a long hiatus, so feel free to check them out to share ideas. I do this full time after quitting corporate about 3 years ago.