Always study a fish before you buy it. If it's fresh, it should look moist, plump, and juicy, and have a little bit of a sheen. Its eyes should be clear, not glassy. If you're detecting a fishy scent, steer clear. A truly fresh fish, whether whole or a filet, should not have much odor.
Gently press your finger into the fish. (Now that you're friends with the fishmonger, he will let you.) If your indentation disappears, you're good to go. And every expert we consulted said the same thing: This is no time to skimp. "It's always worth the couple of extra dollars to get the best stuff," says Prewitt. Basically, if you weasel out and buy subpar fish, all the trickery in the world won't mask its wretchedness – or your own.