Hallmark China’s service was better than expected (see post below – we found out that all Christmas cards that we bought had a price sticker on the back that could not be taken off without damaging the card, and we had to go back to return them). After a short discussion they agreed to send us new cards, although they may be different from the ones we bought.
They told us that all their cards have the price and barcode sticker on the card itself, instead of on the plastic cover. The reason is that Chinese tend to take the card out of the plastic in the shops to take a closer look, and then put them back without the plastic. In that case the bar code would get lost and the card cannot be sold. Strange that this only happens in China, and even stranger that we seem to be the only ones complaining about it (so maybe Chinese really like the recipients to see the high price they can afford to pay for a card?). The cards with sticker we could return, except for the ones that I already wrote on. Good service Hallmark, other companies can learn from this!