What dat?

I made some coin purchases last month at the coin club meeting, from another
club member in a private transaction, not from the club auction. Hard as it
is to believe, I studied this one coin, a Boone half, considerably before
making the purchase. I had noticed three brown toning spots, evenly spaced
on the reverse rim, and they unsettled me a little because they were so
evenly spaced apart. It wasn't until I was back home, though, that I saw
this on the obverse rim;

http://showcase.netins.net/web/bills...ns/whatdat.JPG

Not only are there four tiny dark spots on the obverse rim, each spot has
the slightest indentation into the coin. I suppose this coin has been
mounted in some way in the past, which is briefly what I thought about when
I had seen the reverse rim toning spots.

Would anyone know what method a coin is mounted, or held in a holder, that
would leave such marks?

Fortunately for me, I didn't have enough money to cover my entire purchase
and I still owe 85% of the coin's transaction price. I intend on returning
the coin, explaining why I want to cancel the transaction. Bill

DAT was a chytty thing for the seller to do.