What are my options for activating previously activated Steam games?

I purchased some games second-hand from someone else. I have the original discs, cases and product codes. However I cannot activate the games because they were activated by the previous owner, whoever that is. I get the "Duplicate Product Code" message.
What are my options?
Best Answer
There is no way for you to legally play the games you have bought if the activation codes have already been redeemed. Your only option is to take them back to the person you purchased them from and ask for a refund.
The games and their activation codes are locked to the original owners Steam account and cannot be transferred to your account. The discs you bought are effectively worthless as although they contain the digital files for the game they no longer include a license to play the game, this was redeemed by the original owner and they still have the license and are able to play these games even though you now own the physical discs.
PC games almost always have one time activation codes, once they have been activated, in this case by the previous owner, there is no way for you to activate them again on your, or any other account. To play these games you need a new activation code, this is why there is no market for second hand PC games at your local game store or anywhere else.
Assuming this was a private sale, I don't know how viable an option returning them really is. They probably sold them to you knowing full well they were not playable and you will be relying on them agreeing to give you a refund.
If you bought them from a store then you will be in a better position to return them, depending of the laws of your area.
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What happens if you activate a product on Steam you already own?
If you enter a steam key of a different copy of the same game you already own, your steam key won't be used. It will say that you already own the game. The exception is when the game is included with others game in a bundle, in this case the key would be lost.How do I activate old games on Steam?
Log in to the Steam client application (if you haven't yet, you can download the Steam client here). Click the button labeled "+ Add a Game" on the bottom left on the Steam client and select "Activate a Product on Steam..." and follow the on-screen instructions.Can you use Steam activation code twice?
Each Steam key can only be activated in a single Steam account. You can however login using the same Steam account on more than one computer, but only one at a time. When logged into Steam all the games activated within that Steam account can be downloaded, installed and played on the PC.How long do you have to wait after too many activation attempts Steam?
If you get the error 'Too Many Activation Attempts' when you try and apply a Steam key then you will need to wait for a few hours before you try and add the remainder of the keys.Mass activate free Steam Games | SteamDB Free Packages tool
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Answer 2
You should ask for refund!
I purchased the games (about 10 of them) from the ShopGoodWill.com auction website. I did basically what you said and reminded them that they sold me previously licensed software that is basically useless/worthless. That is all it took. They issued me a full refund.
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