I would do it so that you can buy a maximum of 4 cards from one card in the auction house. (you only need 4 for max uprade). The cards from the booster can stack, but if you already have 3 shamans, for example, you can only buy 1 and if you have 4 or more, you cannot buy any more at the auction house. That means even if you have 4 pieces and put them in the AH, you cannot buy 4 new ones directly, but only when they are sold.
You also have to set a limit on the number of cards that can be sent, if one already has 4, another cannot send him cards of the same type. thus that is also taken out. If he only had 3 cards he would get 1 sent to him. Not more because you just don't need them.
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