If you have a microscope with high magnification, you'll want to examine the rim along the inside edge. Usually, two-headed coins are made by removing the rim of one coin and the interior of another coin so that they will fit together to make a magician's coin.
You can't flip the coin and be the one who calls heads or tails unless you want to get your butt kicked.
I've seen a Kennedy half or a Washington Quarter mated with a Sac. dollar !! It was amazing the accuracy of the tool used . It was almost undetectable by Graders at NGC, I believe . I'll have to look for the video. I think it was on TV though .