The way that fake two-headed and two-tailed coins are made isn't what you'd expect, which is why many people who find them are reluctant to accept the truth about them. They are not made by cutting two coins in half and then sticking the halves together, which is why you won't see a seam along the edge giving the coin away. Instead, two-headed coins are made by hollowing out the center of one coin, leaving the reeded edge and heads side intact, and then shaving down a second coin so that it fits snugly inside the shell of the first. You need a fair amount of skill at metalworking to accomplish this, not to mention all of the proper tools, but the result is a clever deception that is hard to detect with the naked eye.
How to Detect the Seam of a Two-Headed Coin
If you use a strong magnifying glass to look very carefully along the rim of the two-headed coin's face, on one side or the other you'll see a very fine line around the circumference of the coin. This line isn't on the edge of the coin; it's actually on the front (or back,) very close to the rim. This is where the shaved down coin was inserted into the hollow shell of the other.
If, after carefully examining your two-headed or two-tailed coin, you still aren't convinced that it's a novelty item, take it to a coin dealer and ask him to show you how it's made. One thing is for certain, it wasn't made that way by the U.S Mint!