Nope, there is no way to check. It's been a long time since I've done this, but before you could check the validity of the code before adding it to your account (so you could have made a screenshot showing it's valid before selling it and the buyer couldn't have said otherwise).

And there's no point in contacting Amazon to ask them because they won't be able to give you an answer (unless you report it to the police)...
They will tell you they're not responsible for codes stolen, lost, etc...

However, the country is easy to guess, if it's a .com voucher it can only be used in The US, a .fr voucher can only be used in France and so on.
(You can not buy an Amazon.com voucher and use it on Amazon.fr if I'm correct)