According to the book "The Conscientious Marine Aquarist" it says this about Triggers: "I would not be concerned with an individual whose fins are slightly torn or that appears thin. The family is hardy and readily repairs."
From personal experience, lfs don't tell the truth and many working their don't know themselves unless they have had that particular fish. The one post is right, most will just say how big a tank you need when you buy them, NOT when they reach full size. I purchased two clown loaches as the tag said need 10+ gallon tank. Mine was a 12 gallon, so I thought I was good. Well after seeing them get stressed and then doing my research these Clown Loaches would grow to 7" :scared: . I knew then my tank was way to small, but unfortunatley was unable to get them out in time and they died but not before bring "ich" to my tank. I now do probably more research than is needed, but I don't want to have that problem again. After doing my research I will never own a Trigger, as they are just not compatible with the fish I truely want in my saltwater tank.
Anyway, don't get to upset if people do exactly what you have asked them to do, give you advice as to why your trigger was looking the way he does. Your tank is simply to small, and I really believe that's why you are seeing the problems. True, he may have been ok in the past, but he's growing, so now the problem is here. The question is, are you going to listen to your fish. Forget about what we say, just look inside your tank, and the fish will give you the answer.