Just refuse to leave the store until they exchange it. This works especially well when i make my wife do it. They'll never call the cops on a girl!
i am going back tomorrow, i already tried the nice way, so now it is going the hard way. i found a document form the ''consumentenbond''(Consumers Association) which says that when promises about the prodcut made by the store turn to be untrue that i am entiteled to a refund. and since the promised me that they hadn't updated the system version(that i had asked before buying it), which they had because the box had a 2013© while the 7.1 patch which was on it got released in 2014, beside that i know of the serial number that it should be below 4.5, only other explaination would have been that they had sold it somewone patched it and returned it, but they told me so firmly that the wouldn't accept returns of hardware so how could that be possible.
besides this i still have the point of getting an unsealed box which i could use. i might leave eventually if they won't exchange it (however i might say i will stay until they exchange it as a bluff) but i won't go without them having to read their entire returning policy out loud to me.