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If Mick doesn't know he will know someone who will.
My bet is that these are fake for several reasons. First is that these are made from standard S 84/98 bayonets rather than the more common KS-98 bayonet. The wear on the bakelite grips doesn't match the wear of the metal, if these were presentation bayonets as the seller claims then the standard worn grips would have been changed. A bayonet with an etched blade will not have a serial number. Plus the starting price is well below an item claimed to be of this type. The seller's bogus description raises a big red flag also. There is a lot more wrong with this blade than there is right.
Another tip when dealing with auctions is to review the history of the seller as much as possible. I have looked back through this seller's feedback to see what items he normally sells and in this case nothing gives any indication he regularly deals in German military items. From what I saw he sells the typical items you see at flea market type gun shows, mostly cheap .22 cal rifles.
A very good reference is "Seitengewehr: History of the German Beyonet 1919-1945" by George T. Wheeler. Faked blades are described on page 129-130.