These days it is quite difficult to tell fresh sea scallops from imitations, which have been stamped by machine out of shark meat or from the meaty wings of the manta ray. If the market price seems inordinately expensive, the scallops are usually genuine. Unfortunately, it is easy to tell real scallops from fakes only after cooking. Those not real will often have offensive, excessively fishy aromas. The best advice I might give is to buy your scallops from a reliable fishmonger. Or if you are lucky enough to live near that font of fine seafood Seattle, buy all of your scallops fresh in their shells. They are delicious.