About buying and Selling Physical Gold (not CFD)

I understand gold is a stability asset and has always been so. But my question is. When you buy Gold, surely youre buying it at a higher price then the market. And vise versa, when you sell Gold, you surely are selling below the market?

Where do you buy and sell Gold and what are the margins in purchase/sale youre willing to take a hit on?

Im just a noob, so forgive me if my questions are silly