One things for sure, commercial fishermen do not need the hobby angler to tell him where the fish are. They are far more experienced and well informed than we are, they have to be they earn a living from it.
Regarding other nets, anyone can set nets so long as its spoils are for their own consumption. Selling fish without a commercial licence is illegal and if you know of anyone doing this then report them to Southern Sea Fisheries HERE. This is the body that is supposed to police these issues. However with only 5 officers for the whole of our area they are pretty much up against it
Martin