Anybody would have to be really stupid to add a bunch of weight to a fish. I couldn't, but have a bunch of buds that can judge the weight of certain local fish within a few ounces just with a quick look.
I'm sure the local Walleye guys could immediately know something was off.
Fished a few SKA "southern kingfish association" tournaments With a buddy who is a DR, he'd hook up an IV bag with saline solution to the fish. LOL None of those kings were ever close enough to being big enough to win.