I have known a few "scrappers" that did OK... it's a CASH business, so there are a few tricks to the trade... and one of those "tricks" is you're not making any real money cruising the curbs on garbage night.
To make money you need regular sources of scrap.
Metal shops are GREAT for scrap. They have "cuttings" that are clean, the "cuttings" are already written off the books, so you drop a case of beer on the foreman and load up your truck.
Back in the good ol' days of better tax write offs on vehicles, a buddy had a fleet of nice new Kenworths (with BIG motors, road ranger transmissions, 72" sleeper, cool paint job... REALLY nice trucks.... pulling scrap) that pulled the worst looking, rattiest disposable side trailers you've ever seen. He'd drive them for 3 years, writing off the truck price 100% off the scrap sold... then sell the really low mileage trucks for cash... and put the cash in his pocket. He sold 3-4 trucks a year, I doubt he made a dime in metal recycling. All the trucks he sold went logging. Ya can't do that anymore. Damn the CRA.
another guy i know had a lot off Wolfedale where he could park 100 cars. The price of scrap fluctuates wildly... so he'd work his nuts off when the price was low, and no on else was working (there's WAY TOO MANY scrappers) and when no one else is working, there's no competition, so you pay nothing for the scrap cars and he'd fill his lot. When the price went back up, he emptied the lot. He's younger than me, and retired before I did.