Real copper vs copper-plated steel
Copper-colored doesn't mean copper. Plated steel is everywhere, and a magnet settles it in one second.
Where plated steel shows up
Cheap hardware, grounding rods, some welding wire, decorative pieces, older coins and some wire sold as 'copper-clad'. From a photo it can look exactly like the real thing.
The one-second test
Touch it with a magnet. Copper never sticks. If the magnet grabs it, it's steel with a thin copper skin, and it sells as steel.
Confirm with a file
File through the surface. Real copper stays salmon pink all the way down. Plated steel shows grey under a thin colored layer.
Copper-clad aluminum wire
Some cable is aluminum with a copper coating. It doesn't stick to a magnet, but it's much lighter than copper and shows silvery white when you cut it. Yards grade it far below copper wire, so cut a strand before you sort it.