HMRC (Her Majesty’s Revenue and Customs), employ specialist officers who work in the “backroom”.
As far as the eBay bullion market is concerned, the “specialist” refers to use of knowledge and experience gained in the jewellery and bullion markets and they are responsible for successfully prosecuting a range of complex cases from VAT and duty evasion on imported precious-metal products to plain tax evasion through failure to declare revenue from the sale of raw and worked precious-metal products. Jewellers are of particular interest due to the many opportunities available for irregular dealing, but coin dealers and bullion dealers are not unwatched!
An important part of HMRC’s work is the detection of suppliers of counterfeit and forged currency, and the creation of “network maps” is usually the key to the uncovering and liquidation of the source.
This is also the case if you misrepresent the metal composition or falsely describe it; so if you knowingly sell a base metal item as silver, for example, or knowingly describe 9 carat gold as “solid gold”, (in fact, it only contains 9 parts gold to 15 parts other metal, so it’s not solid), or pass off or falsify a hallmark, then you would be rendering yourself liable to prosecution.