These look like blow flies, Calliphoridae (green), and flesh flies Sarcophagidae (grey). I would suggest for good Hygiene, and the customers, the owner needs to keep the fish/meat covered, as they are would laying eggs, and live maggots direct onto his products.
I am not sure that this is his own shop. I don't know what they are, but there seem to be 3 species, the smaller grey ones on the right and top left, two green ones on the left and the larger green fly with red eyes in the middle.
I live in Thailand and all of these flies are also quite common here. I expect that they are probably the same species.
I would have to disagree, flesh flies ( Sarcophagidae)are often larger (although these are smaller in this image) and usually grey-speckled, blow flies are often green/blue, and that is what they clearly are in this picture. Certainly two different species from two different families here.
Certainly two different species from two different families here.
I must apologise for my original unclear comment that "I expect that they are probably the same species". I didn't mean that the flies in the photo all belong to the same species, it seems there could be 3 species in the photo, but I meant that they are probably the same species (plural) as the ones here in northern Thailand.
Not sure what species/genus this Indian blow flies are, but here at this link is a selection of North American Calliphoridae, many look to have blue or green colouration, but some species are black or do have black thorax, which is often the case.