1916 D Mercury Dime In Great

This could be one of those coins where a 16-P (or S) obverse was mated with a D mint reverse. That could explain the seam that can be seen around the rim on the reverse side of the coin.

The OP wanted some "insight" as to this coin. Our red flags went up for several reasons. One question we (naturally) would have is why would someone buy such a key-date high end coin, and then want "insight" to it? It's like buying a Ferrari and then wanted to learn how to drive. If you were knowledgeable about this high end coin, you would know not to handle it with your bare hands. It's like a piece of high end jewelry, and should be handled as such with cotton gloves. So please excuse us when we immediately think the coin is not genuine. And as pointed out, if real, why would a coin dealer not himself have such a rare valuable coin graded by a TPG service? Grading adds value. Everything isn't adding up, BUT we could be wrong, and we hope for your sake you did just get an incredible deal and we are just too skeptical (we do see a lot of fakes). It would be extremely helpful if you would kindly submit better photos of your coin here to us, enlarged showing both sides of the coin. If you are certain it's the real deal, you really should submit it asap to PCGS or NGC to verify it as real and to guard your investment. Please keep us informed, and best of luck to you!

@merclover:

https://www.telegraph.co.uk/motorin...r-crash.html