So what happens if you use a key on an alt account and then claim it was duped?

Report it to support. If it's the first time they can't do anything but if it happens repeatedly they will take actions.

But if it's from one of the Star Sky games from the recent Otakumaker Bundle there were reports of the dev handing out used keys so your winner is probably innocent.

Can't they just delete the old key and give you a new one? That way, no crime will have happened and, that way, no punishment will need to happen. ;P

if it was a star sky key that he said was duped it most likely was as 2 out of 5 of the ones people got from Otakumaker were duped keys its how the publisher sent them not Otakumakers fault or anything:)

tough to prove, but if someone consistently marked GAs as not received, it would certainly attract attention

"...Otakumaker..."

First consider the source. Otakumaker is somewhat unprofessional, so I wouldn't be surprised about getting a dupe key via them.

On the other hand, if this was from Bundle Stars or Humble, I'd be more suspicious.

If you suspect any "funny business," report it to us so that something may be done about it. Do NOT make the same mistake others have by talking about it in the forum or Comments section.

Contact the site you got it from, and ask for a new key while saying they can request to delete the previous one. If the winner was trying to be smart, then he'll be in for a surprise.

Unless you send a gift link there's no way you can really prove it as devs aren't typically going to take the time to check whether an individual key was activated - even if they did there'd be all sorts of shit brewing if they then went around telling any old person who redeemed a certain key (they can check if a key was redeemed, I don't know whether they can see to which account).

IG links note the email address they were redeemed to, HB ones don't but if you sent one to a given address Humble support should at least be able to confirm the link was redeemed by the same address, Neither of those will guarantee the same user then redeemed the key after receiving the link but you can at least show the support staff here that they received the link . It being a link also means that even if the key ultimately is bad shows that you can't have tampered with it as you never saw it.

Yeah, i've won a GA a couple days ago and the key was duplicated. Asked the support how to proceed what they never answered. I spoked with the person who created the GA and told me he was sure it shouldn't be no problem, but still, couldn't activated it :.
I won't risk my reputation (though i'm new) for a key of a game.