Do you know how to tell gold overlay vs solid 14k or 10K?
24K is the purest.
18K, 14K, 10K, are all composit, but with less gold.
The color is different.
Overlay is different from gold plating. Overlay is a pure gold exterior with either a nickel or bronze inside.
Plating is usually an extremely thin coating of gold. It looks flat to me, not as rich in color.
When in doubt, hold the peice up to a peice you know is 10, 14, or 24K.
Stamping is regulated by Federal Law. Peices are usually tested to confirm they are stamped properly, and if a peice seems too good to be true, ask if it is an overlay or plated. If they don't tell you the truth, the Feds will crack down on them.