Darren72,
You say your experience at I&S "wasn't all that great". But you say that "the vast majority of the fish seemed very fresh". And "the prices are excellent".
???
I say, "get the fresh stuff". Don't get the not so fresh. You have options.
I'll give you an example. Recently, Stanley's produce place has been my go to place because they have such a great selection at good (mostly) prices. There are times, however, when you can't find a decent head of romaine, so we either do without or find it elsewhere. But that doesn't make it a "not so great shopping experience". If I have to have that lettuce, I know where to find it. It's at the store that sells the $0.99 lemons.
I often buy cherrystones at I&S, but when they aren't up to snuff, I'll go over to Rubio's, where there is maybe 30% of the selection of fresh fish available across the street, but usually fresher clams.
Have you taken a good look at majority of the I&S clientele? These aren't people dressed in the latest designer clothes, but they are folks who are happy to find a great variety of fish and shellfish for their ethnic dishes at a good price. And these folks know more about freshness of seafood than the suburbanites buying shrink wrapped farm raised salmon at the Jewell for $13 a pound.
Regarding the freshness of shrimp and clams at I&S: I believe that the problem might be (just an educated guess) their practice of mixing old and new product in order to give a more abundant look to their self serve bins. After a few days of mixing old and new, with the customers digging around mixing things up further,
it doesn't surprise me to hear that occasionally, a few of the shrimp are off. A better, yet less impressive method would of course be to sell the old and then present a more impressive display of the newer stuff.
I&S is my go to place for cod, swordfish, whole skinned catfish, and occasionally whole, dressed croakers for pan frying. If I want a piece of pristine wild salmon for curing or live soft crabs, it's F&O, but I walk in knowing that I'll be spending 25 bucks a pound for the salmon and $6 each for the crabs. Money well spent. (No more soft shells at Whole Foods

) I also love the experience of going to a fish market like I&S, that carries maybe 12-15 different types of fish in the round, and another 12-15 types of fillets.
Rubio's is my go to place for canned pasteurized crabmeat, clams, and I get their 16/20 shrimp in 5# boxes. I'm not impressed at all with their fish selection in terms of options.
I'm glad to have both I&S and Rubio's nearby. I can't imagine getting my seafood where they sell those $0.99 lemons.