Ah yes, the oldest trick to mess with the weight. But if you learned how much he did pay for that fish, you wouldn't ever buy at a shop near home ever again. Why not get closer to the source, or, fish it yourself?
In my country, the price of one fish in the city is like 50~100 fishes near the shore. Getting angry for something this small when you are being ripped off for buying there in the first place is pointless. Of course he will tell you its to keep the shop running, fish needs to be refrigerated, etc. There is also transport, wages, taxes, blah, blah.
So cut the middle men and start fishing already, you may even enjoy it.
Actually I'm in a position to know how much is generally paid for fish by the particular company...
It varies a lot but they pay around 60% of what they charge for retail. And they have to throw away a lot of stuff too. I understand that people have to make a living and companies have to make some profit from the products they sell.
You'd be surprised how all the costs add up for groceries running seafood departments. That's why full service seafood counters are rare in supermarkets in the US nowadays.
If you go to a walmart I doubt they even have a seafood counter, probably just nasty pre-wrapped fish that was previously frozen and then thawed for display.
And while properly frozen fish that were vacuum packed are good, fresh is just a little better. Of course unfortunately it's very few fish that can survive fresh for the days required for transit and still maintain good quality.
And yes I'll start fishing, might as well. I'll start with freshwater. Maybe get some bass and see if I like them.