If you want to learn about a really interesting aspect of the "first sale doctrine" and how it applies to software, you should have a look at "Vernor vs Autodesk" in the USA and compare it to "Oracle vs UsedSoft" in the EU. Basically, in the USA the courts determined that if a company sells you software, but in their terms & conditions claim that they are merely granting you a license, then you can't resell the softw…
Most mobile apps have moved to a model with in-app purchases. I wonder if this rule applies there. If a game is free, but I spend $1.99 on 500 gold coins (in-game currency), does the law require that I be able to sell the gold coins? What about if I use them to buy virtual non-consumable items (like permanent character upgrades)? I assume the law wouldn't apply to consumable items (like spending 50 gold coins to spee…
As far as reselling unused in-game currency like gold coins that speed up construction of a building, I personally think it would be cool to see a secondary market pop up. However, I don't know if that would be covered by UsedSoft v Oracle.
The big question is whether individual Steam games should be able to be resold in the EU due to Oracle vs UsedSoft. If so, that's a potential multi-billion dollar secondary market that doesn't exist yet.
Edit: Sidenote, I actually started an auction site based on the idea of reselling Steam games (and ios games) several years ago based on the UsedSoft v Oracle ruling but due to these companies not allowing users to transfer licenses between each other, my startup was not workable.