Get there at the start of the dinner hour (when many French and American chefs go for a bite before heading for their own restaurants), and sit at the counter. Early arrivals tend to get more personalized service and fresher fish. Inspect the seafood: Is it covered (or at least wrapped) and kept cold -- or has it been gathering flies since the lunch hour? If the latter, leave immediately! Start with an order of uni (sea-urchin roe). Its flavor gives away its age: It starts out a bit briny, like a very mild oyster. After about 12 hours the brininess intensifies -- it's still edible, but no longer ethereal. After that, an iodine note grows ever more prominent until the uni turns bitter, rusty-tasting, and potentially indigestible. The second "tester's choice" is a scallop hand roll. Not only are over-the-hill raw scallops gross-tasting, but poorer grades are preserved in a phosphate "brine" that gives them an opaque white color, a mushy texture, and a sheath of filmy white liquid. Small "bay" scallops may exhibit similar adulteration; many are actually low-grade large scallops, sold chopped. Top-quality scallops suitable for a sushi counter taste clean and sweet and have a translucent ivory or pinkish color; they may be tender or firm but not mushy or slimy. Their quality and freshness will be as evident in a hand roll as on a nigiri, but the former will also let you assess the chef's skill and palate when you taste the mayonnaise-hot-sauce blend -- and when you lift the roll to start eating. If the cone unravels, your chef's an apprentice.