Did I get taken advantage of?

Thanks. Carbon dating will not work for authentication of coins, because it only works on organic materials, not metals. But as @Nathan401 indicated, we have lots of scholarship to fall back on to authenticate coins. One learns to recognize things that are "off", and develops an instinct for this sort of thing. I'm not saying it's perfect (no human endeavor is), but a little bit of knowledge goes a long way.

For myself, with 40 years of numismatic experience, I find I still have much to learn. My knowledge is pretty broad and covers a fairly wide diversity of coin types, but it doesn't run particularly deep compared to that of the more specialized collectors. Some folks specialize in one particular type or series of coin. As my "Eclectic Box of 20" indicates, I'm more of the proverbial "jack of all trades and master of none". (Well, I do have deeper knowledge in some areas, but certainly not all of them. Nobody knows it all in this hobby. That's what makes discussion boards like this so helpful.)