Don't read on until you have made your choice!
At the top, a stamp sold for 20 €uro in the recent www.filateliapalvelu.com auction.
Underneath, another Lot unsold at the starting price of 60 €uro
As far as I can tell from the scan of the first Lot, the basic stamp is from the later ( 1890) printing of the 10 kopeck which has different basic shades compared to the 1872 printing It also has a later-style R.O.P.I.T cancellation. So the overprint (which was issued in 1876) can't be genuine. (These later R.O.P.I.T cancels also exist in forged versions, described in Tchilingirian's work, and these forged versions turn up on things like the 1918 so-called "Beirut" R.O.P.I.T overprints)
The second lot (which I put up for sale) shows the shade of basic stamp you would expect for the 1872 printing and three stamps are signed by the late Eric Peel, who knew about these overprints.