While reading a blog, I felt compelled to discuss an overlooked end result of the damage caused by counterfeit coins. As we are all aware, EBAY has become a very hot topic as related to counterfeits, specifically the knock-off "genuine" slabs or the oddly named companies such as NCS, the most common of several. But this is not to leave out the uncertified coins from the subject as there are many at any given moment selling. Finally, this is not to exclude coins sold through dealers, both local shop and online, as well as coin shows.
The purpose of that first paragraph, especially the most popular source for buying coins, particularly new and young collectors. However, the following applies to all collectors. Not only are counterfeits destructive to the market as a whole, the sale of these worthless hunks of metal end more collections as those being taken simply give up. Think about that for a moment. How many new collectors, those on a budget, has this stripped the hobby of? Given the popularity of the auction site and the continual rise in those trying to make a quick dollar I'd surmise it would be a high number.
Therefore, may I offer a bit of sound advice. No matter which avenue you buy your coins from, if the deal looks to good to be true it probably is. Carefully look at it closely, if possible in hand or extremely clear photos. Compare it with like graded coins from sites such as NGC or PCGS. This should apply if the coin is graded as you can check it's certification record. Never buy a raw coin above $100 dollars unless you are very confident in your knowledge of said coin, and under no circumstance buy in the thousands. As for graded. Buy only NGC, PCGS, ANACS, ICGS or PCI as these companies guarantee authenticity. Grade, however, is another subject.
The absolute key to not becoming a victim is education. Simple research, a few good books and organizations such as the ANA are essential.
On a side note, not long ago I saw a slab that at first glance looked exactly like an NGC. Except for the same color and font NCG next to the scales. Did you catch it or have to read that last sentence twice? Be very, very careful out there.