I couldn't tell, I just know one has to be careful on these. That's how you have to buy them, though. Hey, I'm glad you didn't say eBay.
Beautiful coin. I understand it is one that is counterfeited a great deal. It looks real to me, but what are the markers of the counterfeit? Below is a fake:
It's sea salvaged, most like from the wreck El Cazador, as the majority of coins from that wreck are dated 1783. They are very common, but yours is nicer than most examples. Value wise, $125-$150 is a fair range if it were certified as coming from that wreck. As an anonymous sea salvaged coin, maybe $75.