You can google it before you buy you know:
http://us.blizzard.com/en-us/company.../wow_eula.html
And you can have a refund as long as you have not used the item you bought (At least here). If the boxed copy/game time card is unscratched, then you would be able to get a refund just fine.
But as soon as you open the box or reveal the code, the item is then used and can no longer be refunded.
When you buy online, you get the code attached to your account as soon as you pay, so it's instantly "used".
Want to try the game without any strings attached? Oh look, a wow trial account!