OBTW, there was a thread recently started in the General Discussion Forum asking whether anyone keeps the boxes for the knives that they buy. I do because I'm a collector and pack rat by nature.
However, "the box" is not just something you need to decide whether to keep or not. It is, in fact, an important piece of evidence towards proving the authenticity of a knife.
There are fake boxes as well as knives but, just as they fail to perfectly fake a knife, they also fail to do so for the boxes.
I'm not sure if this is intentional or simply negligent but the differences between a faked and factory box (if you've seen the factory boxes) is pretty obvious -- most notably in the coloring and labeling, especially the description/model # designation of the knife usually on the box end.
This is less of a problem for older/discontinued knives that are not in high demand that the fakers cannot make much $ on unless they are very expensive knives where the volume of sales doesn't matter as much.
Anyway, these are the reasons why I generally will NOT buy a knife (especially on EB) unless the seller has the box and has posted (or sends me) at least a picture of the box end.
I have bought knives w/o boxes but I know I'm taking a risk doing so and, if the knife is expensive, I spend a little more time to assess the authenticity of the knife and the reliability of the seller on top of taking the consumer protection safeguards mentioned above to make sure that I can return the knife if is a fake or otherwise not as described.
As they say, "caveat emptor."