Good evening, Mr. Evening.
I usually buy my game cards through Taobao and its pretty simple. I usually go for the automatic charging option where you just enter your battle net email login and game account name (WoW1, WoW2, etc). After you pay, it should then automatically credit your account with the amount.
The other option I've used is the automatic delivery where they give you a card no and password in the transaction details section after you pay. Then you visit the stated website, enter all the details and it credits your account.
Both options seem to work really well.
I also know that Pwn's wife (Feis in game) runs a Taobao store that sells game cards if you want to discuss with him about it.