They will be more likely to charge you if you have 2 and one, or both, is still all nicely wrapped in the box and unused.
Grant has found it depends on who you get as you come in as to whether they charge you or not. He brought back a lot of electronic stuff, had the receipts and all the paperwork but they just waved him through, even though he had several hundred dollars worth of stuff and well over the limit for not being charged.