Selling gamecards for gold ?

Q u o t e:
this guy was spamming in trade "WTB 60 day gamecard 5k gold pst!"

is that allowed in WoW?

This particular transaction would be seen as an exchange of real-world items for in-game currency, something which is currently against the Terms of Use. For reference, the related section of the Terms of Use is available here:

http://www.worldofwarcraft.com/legal/termsofuse.html

Q u o t e:
Blizzard does not recognize any purported transfers of virtual property executed outside of the Game, or the purported sale, gift or trade in the "real world" of anything that appears or originates in the Game. Accordingly, you may not sell in-game items or currency for "real" money, or exchange those items or currency for value outside of the Game.

Q u o t e:
so...report it?

Absolutely. In-game petition or an email to [email protected] will do just perfect. :)