I could make a good argument using the sale of a $300 fake for $17,000 + commission at auction last year, but I would probably get another letter from the auction proprietor... The only good thing about ebay: 1) Normally fakes are obvious, like this "Novodel" -- just ask for better photos; 2) The coins carry smaller price tag in comparison to auctions.
However, the fakes that scare me are the ones that we cannot recognize so easily. It appears that high level forgeries have been sold by auction houses in US (and, at this point, I will say ALL auction houses) and abroad. Good examples are 1704 rubles, 1741 rubles of Ioan, Yefimoks, fake copper patterns and novodels, 1728 rubles, all sorts of commemorative coins, coins with plain edge, overstrikes (1796 em, 1791em, all 5 kop and 2 kop am's). You got a factory in Rostov producing high quality fakes. You got an outfit in Moscow that sells 1704, 1741 rubles for $150 -- 300 a pop, which were actually sold for huge amounts of $ at auction here and in europe. You got a ukrainian outfit that turns out copper pattern and novodel fakes. These things (good fakes) have been made since as early as 1980's. A fake 1712 ruble traces back to a 1991 SwissBank sale. By the way, it was graded by NGC, and later sold at 3 successive auctions culminating in a $18,000 price tag...
Sometimes it feels that it is a miracle to buy an original, no matter what you are paying for it...