nothing a quick format doesn't solve, but yeah in most cases stores are happy to do exchanges....less happy to do refunds, they will normally just push for a gift voucher refund unless you stand your ground
Ah, true for the quick format.
The problem with exchanges in this case is that... well, they need to have another N3DS within the correct "serial range". You should be able to find some for now, but more you wait, more complicated it will become.