That gun has been up on GunBroker for over 2 months and he still has not dropped the price...says something to me about the asking price.
I believe it is a Bayard model 573 which uses the Anson Deeley design. Exactly how long Pieper produced this design I am not sure, but I believe he started marketing it some time after 1900.
Of the marks I can clearly see:
12 in a Circle is the gauge designation used in Germany 1891-1939
Crown over N is the nitro designation used in Germany 1891-1939
Choke markings used in Belgium 1910-1924
It as also shows a superior Belgium proof stamp on the barrels. Which means it passed a heavier proof load than required by Belgian law at the time.
So, by the proof marks, some time between 1910 and 1924. Which makes sense to me. I am guessing it was made for the German sporting market post WWI. It has the traditional sling swivels. So it was used as a hunter at one time or another.
On a side note, Henri Pieper was actually of German descent, which most people do not know.
Pricing for it? No one has even bid the opening bid in all the time it has sat there. I think the seller is off by about $1,000. It is a nice English clone, however, if that is what you are after for that price there are plenty of real English guns around.
Pete