Yup, I always do that to check the board's stiffness.
I've never gotten a board to flex as much as the guy in the video, but I'm usually looking at stiff boards.
Actually, the sales person usually does that in front of you to show the board's flex. You didn't have that happen when you bought your board?
No I did not. Even if I had bent it, I wouldn't have bent it as much as he did. Next time round I buy a board, I think I might. But I think I would step on it and bend as much as he did only if I have already paid for it.