In general B Stock refers to any product that has been sold or titled to another entity for a brief period of time.
A customer could buy a receiver, decide that the color of the case is not to their liking, and return the receiver.
A customer could buy a receiver, the unit have a problem (real or imaginary) and return the unit.
In both cases, the manufacturer (OR an outside vendor) will process the unit, make any required repairs, repackage the unit, and sell it as B Stock. the repackaging is suppose to identify the product as a B Stock item, but not all manufacturers have a clear identification process of their B Stock.
Can B Stock be misrepresented as A Stock? You bet. And it happens quite often, especially with firms of questionable ethics.