Looks suspicious to me with what appears to be cast Pitting although I'm no expert.Highly concerned about it,grade estimate if real to me VG details.
It looks like a cast replica to me. The pitting and the apparent casting metal flow on the bottom of the coin really screams fake to me.
I don't know what to think about it from those images. You can't even tell if it's the week S mint mark because of the damage.
Is it being sold by someone reputable located in the country? If it's real I'd guess it would go G6, Details. Better pictures might make it easier to assess. There were only 8000 of the 1866 minted, so there's a good chance it's an 1866-S with the S obscured by damage, I'd buy it (again if the seller is reputable) only if you could return it as a practical matter, and get it assessed by one of the four TPGs immediately to get it authenticated. I'd use ICG initially as they are fast, affordable and fair, and then if you were worried about value I'd submit it to PCGS later if it proves real.