Selling Gold Question - How can I tell if it is gold?

[Sweety_tweety]

I am going to try selling some old gold pieces. I have read where gold pieces are stamped.

What if there is no room for a stamp? How can I tell if it is gold? Do they give you anything if it is gold plated? I have what I believe is a thin gold bracelet in bad shape and also shell shaped pendant that I want to sell. Thanks for any advice.