The way I tell is how it is packaged when I'm opening it up.
1 is the factory "retail box 'factory' sealed?" Or does the tape look redone?
2 How the item looks in the box, most factory packed goods are so neetly wrapped that if you or I were to repack it, it wouldn't quite look right.
3 the ties on the cords are another good indication.
4 Finger prints. Most packers use some type of gloves so as not to soil the item in any way, next new electronic you buy look this over very carefully!!
5 Manuals. they are actually placed very carefully the thier exact spot where they should be.
6 Tape on over wrap, once opened it won't reseal woth a darn. Also overwrap will be wrinkled if it has been handeled before you get it. Most people tear the overwrap when opening.
This is not all inclusive, but I've opened over 2000 electronics in my life time and you can tell after awhile if you get a "reship"
No need for concerne as long as every last thing thats to be in box is in the box/package, Warrenties instructions also item baught.