You do not need expertise to order seafood well. You need about three questions.
Ask what is good today
The single most useful question. Fish availability changes daily. Anyone who tells you everything is equally good today is not paying attention.
Ask how it is cooked, not just what it is
The same fish grilled, tandoored or curried is three completely different dishes. If you like clean flavours, go grilled. If you want depth, go curry. If you want smoke and char, tandoor.
Match the fish to the treatment
Delicate fish (pomfret) — keep it simple. Grill it, butter, lemon. Burying it in spice wastes it.
Meatier fish (rawas) — stands up to tandoor and stronger spicing.
Prawns — go with almost anything.
Crab — always more work than you expect. Order it when you have time and do not mind using your hands.
Do not over-order
Seafood portions on this coast tend to be generous. Two mains and something to share beats four mains and waste.
If you are with people who disagree
The Seafood Platter for two solves the "we cannot decide" problem. See the full menu.