IMO, subs are the hardest thing to judge by in-store demos. No peice of gear is as room-dependant as a sub. Often I hear someone criticizing a (subwoofer brand here) sub, and I can tell just by reading his comments that the sub wasn't set up properly. The problem is that even a great sub can sound really bad if it's not set up right. Likewise, a savvy dealer can choose material to play to the strengths of something he's trying to move.
That said, if there's any peice of gear you could safely choose just from reading competently done reviews, it would be a sub. Not that you should ever make your choice that way.