[US] Could this be a Amazon Gift Card selling scam ? If yes, then how ?

Somebody on WhatsApp is selling Amazon gift cards for 40% discount. This is too good to be true.
How are they trying to defraud ?

Could this be a stolen gift card or a blacklisted one or something bought with a stolen card ? I am defintely not going for it just trying to wrap my head around it.

Also, I got a couple of gift cards from my friends for my birthday, how do I check the authenticity of these gift cards before loading them on my account ?

I have been a loyal prime customer for years now and I certainly don't want to mess up my credibility with Amazon for a few free dollars.

Need your opinion folks.

Thanks.