It is typically not that hard to tell. If the box has uneven double taped seal, it has likely been opened and re-closed. Likely the original tape was put on by a machine, and the re-seal was put on by hand, and less likely to be smooth and even.
Also, though the seller should have been honest, a box simply being opened does not mean the speakers are used or in anyway lesser. It doesn't necessary not mean that either.
Curious why you are asking?
Steve/bluewizard
There is a hifi specialist not far from me ( sell tellys aswell)
Everything you buy from there breaks down after a while and I think they only sell refurbs/repacked gear BUT what really pees me off is that they won't budge from rrp........ their customers are easily conned, Never mention that its not brand new " ever"