Fake Diamonds?

It is hard to determine, at least from a far, real diamonds from fake ones. Oh the you would probably drive yourself crazy if you are presented with a small container filled with loose diamonds but I bet you won't be able to figure out which is real diamonds from the fake ones if diamonds and real gems albeit in their colorless forms like sapphire, zircon, beryl, topaz and quartz were mixed in. One sure way to test if the stone is real diamond or not is to check its clarity. If the stone is mounted you should not see not see the bottom of the stone looking from the top. If it's a loose stone, turn it upside down on dot. If you can see the dot,then the stone is not a diamond. Why the heck am I so concerned? Someone attempted to sell me a faker.