There has been a reported incident in China which included a number of jewelry stores which received millions of dollars worth of skillfully manufactured fake gold jewelry; as well as fake silver bars none of which exhibited uniform weights branded with the Engelhard signature identified in Europe and America.
The fraudulent silver bars are not associated with China; the message here is that the precious metals industry is suffering from global crime schemes increasing in volume and sophistication and therefore requires a certain amount of skill in determining what is and what isn't real gold and silver.
  For purchasers of precious metals of high value; it is best to establish a working relationship with reputable dealers and as for jewelry the same applies, shopping malls and similar related businesses is now highly suspect.
If you are going to purchase precious metals in any form use due diligence or vetting to insure that you do not become the victim of precious metals counter fitters.
For the do it yourselves purchase a simple acid test kit for jewelry and follow the instructions carefully; this approach will yield positive results regarding jewelry purchasing.
  In conclusion; once you have learned to use the kit properly, take the kit to any jeweler you intend to purchase jewelry from and if the proprietor has an issue with your testing before buying, engage that proprietor with reasonable questions as to the importance of the process which you have chosen to protect yourself; and if the proprietor still has a problem with the your demand find a proprietor who will meet your demands.