They're probably just exercising their Right of First Sale. This basically means that after someone has bought an item, they are free to do whatever they want with it, including resell it to someone else. Likely this company has bought packs of WoW at wholesale and is repackaging them for the retailer.
It's perfectly legal, but you can't guarantee that the packs weren't sorted through before repackaging. To be fair, this is true of almost any retailer unless you're buying a sealed case. What you have to ask yourself is what marginal benefit they would gain from adulterating the packs in any way. Is it really a good use of their time to open the packs and pull out valuable cards when they could just resell the sealed packs and not have to worry about dealing in singles?
The hands of a healer