Sometimes a gourmet seafood store, even if they have dozens of varieties for sale, isn't as good a choice as the corner market, simply because fewer people may shop there. If you shop at a place with a lot of traffic, you are guaranteed a high turnover, which almost always guarantees fresh fish. On the other hand, just because your supermarket does a bustling business in every other department doesn't mean they sell a lot of fish. A good way to tell is simply to watch the seafood counter while you shop. Crowds, especially discriminating ones, can be a good sign.
Presentation is key.
The counter and surrounding areas should be sparkling clean, without pools of murky liquid collecting. Pools of murky liquid are also bad signs when collecting underneath the fish. Watch the counter people in action . Odor is also a telltale indicator . This is what you should smell.