I want to buy gaia gold at an online gaia gold shop. How can I choose a safe gaia gold shop

You cannot buy Gaia gold. There are no "safe shops". If you're found "buying gold" (which you're just going to get scammed out of cash), then you can be permabanned. You can, however, use your money to buy Gaia Cash directly from Gaia Online, and sell the items on the marketplace for gold.