A shop saying it is 'Silver' does not mean it is Sterling Silver 925, it means it is Silver of unknown percentage, below 925. German silver is around 800.
Many times an item has aged, a Gold Plated Silver Core object, will have the heavier gold actually sink below the silver, leaving a golden haze on the surface. They can be polished to brighten the silver and remove any remaining gold discoloring the surface or by electroplating them again. This is actual truth, if you care to ask another Jeweler.