To my mind, a commercial is a water which has stocks maintained at a density which could not be sustained through natural recruitment - an artificial fishery.
Natural stock densities for mature lowland coarse fisheries are in the range of 250kg/ha for a gravel pit to 350kg/ha for an estate lake and 500kg/ha for a rich farm pond. Commercials are usually stocked at 800-2000kg/ha.
A put-and-take trout fishery is also a kind of commercial, though usually they need stocking artificially not so much because of unsustainable stocking densities but rather because they lack spawning habitat, are not year-round habitable for trout or are only stocked with rainbows or triploids.
Maybe hard to precisely define a commercial style fishery, but not hard to spot from above