If you are selling coins or bars and the purity is not in doubt, you can get the current available market price.
However, recognise that banks will not buy your gold back from you.
Chances are you will have to go to a gold merchant, or a jeweller.
Many of these jewellers might charge you a hidden transaction fee - they will not pay you a full price for what your gold is worth.
Also see: Invest in Gold through ETFs