How do you tell if your local authorized dealer ..

Call the company to check the serial #'s, if they are without disclosing it to you, they could be committing fraud, and you might have legal recourse.

An authorized dealer should be ethical enough to tell you.
If you bought something that seemed 'used' or was a demo, and the dealer did not tell you... well, they might try it.
"B" stock is actually marked on the boxes from the manufacturer as such (at least the major Japanese manufacturers.)
The manufacturer can tell you if it is "B" stock. The cannot tell you if it was a demo, or a customer return.
Demo stuff or an item someone demo'ed and returned is a bit of a gray area... I would want to know, but I think the dealer can sell it as new. (though the dealer SHOULD tell you...) It certainly has the new warranty.

Well, if its ARC, you can look at the box. There is a big checkbox that says "Factory Refurb" or something like that. Other manufacturers might do the same thing...

All the box are brand new sealed when receiving with dealer ship to address,dated shipped, date to received by Fex Ex, so I am pretty sure they are A stocks. Thanks for the infos.

Call the manufacture of the product.