It is a crazy situation, and this was probably a bad approach for MS to take, but let's keep in mind the real problem here are the thieves who stole all these codes and then sold them to the unknowing rest of us. I see too many people complaining about MS/Amazon/Nvidia and not enough criticism of the real assholes here.
(And for the record I paid $35 for my copy, which seemed like a legit price for a legit good, and this was before the Amazon glitch was public knowledge. People who paid freaking $7 obviously knew something was up.)
Really sucks for those who bought them when there was no evidence of abuse. That's a standard typical second-hand market, just like someone who sells off a physical copy of a game they got in a bundle. (and you can't even resell digital).
Heck, Newegg was giving out the game to some customers who bought the game before the promo started. I even bought a 1070 too, just too early it seems.