You can search the web or look in your local phone book.
Do a Google search.
You can find coin dealers at coin shops, coin shows, antique markets, and through online platforms such as dealer websites or online marketplaces. Additionally, you can check with local pawn shops or visit numismatic societies for recommendations on reputable dealers.
An 1851 2.5 dollar American Eagle gold coin recently sold for $232.01 on Ebay. To find a reputable coin dealer, look for one that is industry certified. Look for dealers that are affiliated with the American Numismatic Association (http://www.money.org/AM/Template.cfm?Section=Home) or the Professional Numismatists Guild (http://www.pngdealers.com).
In order to set up an authenticator with a battle.net account, you first log in to your account. You will find under your World of Warcraft game the option to add an authenticator. It will ask you to fill in the serial number found on the back of the authenticator. Once this is done, the process is complete.
The only reference I can find to a Claudius II Gothicus coin in a British coin catalogue has this description - Possibly a silver coin with IOVI STATORI on the obverse. It may fetch anything from £8 to £20 GBP. A reputable coin dealer will be able to give a more accurate valuation.
A reputable coin dealer will be able to value your coin. If the coin has been circulated, you might be lucky to get 50 pence for it.
Bring it to a reputable coin dealer and they will identify it and give you an opinion on its authenticity. Most coin dealers will not charge you for this service.
The purpose of an authenticator is to provide an extra layer of security
An authenticator is a person who authenticates something - who proves something to be authentic - or a condition or feature of a thing which makes it authentic.
revealing an authenticator over the phone
If you are unable to locate this specific coin at a local coin shop, two very reputable coin companies may have this coin in their inventory: Heritagecoins.com or Littletoncoin.com.
There are many gold dealers that specialize in gold coins for sale. If someone is looking for a gold coin at a good price you can look on auction sites such as eBay or a reputable dealer such as Midas Resources.