It is vital that you buy gold only from reputable jewelers and check the manufacturers registered trademark on the piece itself. These trademarks are registered with the U.S Patent and Trademark Office and can later be verified. Underkarating - indicating more gold content than actually present- is sadly a more or less frequent event in “bargain deals”. Don't trust any piece of jewelry not properly marked with the manufacturer's trademark; this is supposed to be stamped next to the karat mark on the back of the piece. If you are buying an expensive piece or aren't sure of the marking, send it for testing. Exact gold content requires assaying, but simple underkarating tests can be done rather simply and without damaging the piece. There is also a ‘streak test', but this requires gouging a deep scratch in the body of the mounting and should be reserved for very expensive pieces or verification of a piece you have already bought.