A:
Yes and no... but most of the time yes.
My wife and I share one fitbit scale. Adding another account/user to the scale simply requires you to go to fitbit.com and adding email addresses to the scale. There's instructions on how to do this included in the box.
The scale has always recognized me with no problem. But for some reason, when my wife uses the scale, it displays her as "Guest", about one out of five times, rather than her account (initials).
I would recommend buying the scale from BestBuy and keeping the receipt. If you dont like it, they have a pretty good return policy... I think 14 days. You may want to check with your local store.