I agree with the soft-shell/lobster meat thing. Soft shell (referred to as "new", as in new shell) lobsters will fill up with water as you cook them, even if you're steaming, because they have not yet grown to fill out their shells. these are often up to 3 bucks less per pound, at least in areas around maine, because no one really wants them, and purveryors often unload them, despite less profit, on unwitting customers, as they know people will always want the hard shell. due to the newness of the meat, the lobster in a softer shell often has sweeter meat, but not noticeable enough to warrant foregoing the better overall old lobsters.
you can either sqeeze the thorax or ask the purveryor, if he is an honest man/woman.
word to the wise, however. if you get a hard shell in the middle of winter, you will likely have to break out the sledgehammer, or some serious crackers (i recommend those made by OXO).
for live lobster delivered from maine, i recommend the Harbor Fish Market, who delivers overnight.