Ask if your jewellery is hallmarked. IT IS YOUR GUARANTEE
In the UK it is illegal to sell or describe any item as Gold, Silver, Platinum or Palladium unless it is hallmarked.

A hallmark applied by a UK Assay office is not proof of origin or place of manufacture of an item.
The hallmark of a UK Assay office [whether applied by a UK Assay office in its approved locations in or outside of the UK] is a proof that an item [in all its parts] is of the standard fineness indicated by the hallmark struck on that item. 
Hallmarks applied by the UK Assay offices at their approved locations within the UK are clearly differentiated from those by the UK Assay offices in their approved locations outside of the UK [as detailed in the table below]