Question: Ok to sell extra Origin/Steam Keys from Amazon on eBay?

Hi,
See title. I was wondering if is is legal to sell duplicate keys I have from Amazon.com on ebay. Or would I be violating the ToS of Origin, Steam, Amazon or eBay?
My intuition tells me it's ok, but I thought I'd better ask first.

Cheers,
James Joyce

Nobody has an opinion on this?

Still nobody? If this is the wrong forum to ask this question, could a mod please move it to the proper one? Thanks