Faked Coins? How To Tell?

I don't know if there's a single website which will describe all known counterfeit coins, but here's a couple with which to start:

http://rg.ancients.info/bogos/

http://www.24carat.co.uk/counterfei...nsframe.html

There's a lot of counterfeit collector coins coming in from China these days. Many can be detected by a quick comparison with photos of known genuine coins. Others can be detected only by weight comparisons which means one needs to be familiar with an authenticated coin. It used to be that only very valuable coins were counterfeited, but currently, more common older coins are being faked. The bottom line is to educate oneself with a particular series before purchase.

Here's a few more links

http://www.stujoe.com/numislinks/Counterfeits

Nothing that will teach you everything you need to know, though.