The main difference between a numismatic "expert" and a novice collector is knowledge of the technical information used to make decisions about rare coins and notes. That knowledge is indeed specialized, but it certainly isn't always rocket science!
I'm always interested in learning of diagnostic tests that can be used in the detection of counterfeit coins - we don't have too many fakes / duds / counterfeit or forged coins circulating throughout the Australian numismatic market, but there are small numbers of rather crude items offered for sale, and others that take a little more grey matter and knowledge to detect.
Not only that, but we are also but one country in the world, so counterfeit coins issued by other nations can also be offered for sale here. These can be more dangerous again, simply because local collectors will find it more difficult to build the body of knowledge required to know what a "true" coin looks or should look like - impossible to do without being exposed to a lot of coins that can be studied.
An article just posted on the NGC website highlights just one of the diagnostic tests their experts use to assess whether a coin is genuine or not - to check the depth and sharpness of the fine detail evident in the coin. I can think of several reasons why a counterfeit coin may not show the same level of detail as a genuine coin - the dies or mould used to produce the coin may not have been prepared to the same standard as the genuine dies (and invariably they are not), the counterfeit coin was cast rather than struck, or the engraving used in the production of the counterfeit was inferior.
The example images used in the article on the NGC site are of American coins, so you may not initially think they will be useful to an Australian collector. Take the time to read it however - the method is still the same, coins are coins at the end of the day. Building up real knowledge such as this is what sets apart the successful collector from the hack, and will reduce the level of risk you face in building your collection. Re the images below, the first is the genuine coin, and the second is the counterfeit - can you tell the difference?