Danzig Stamps With Fake Overprint

Two stamps I want to buy. (Danzig 1930 Scott 208 and 209.
I am not sure if the overprint is genuine.Thank you for help.

The two stamps should be the same size so I assume you scanned them separately.

They look good. The overprints were printed by Buchdruck (Typograph). There are two characteristics you can look for (applicable for any Buchdruck overprint):
1. The letters typically have an outline slightly darker than the middle of the letters. This is due to the squeezing of the ink to the outer part of the letters as the metal typeface is impressed into the paper.
2. You can frequently, but not always, see an impression of the overprint on the back of the stamp. Not ink, just a slight raising of the paper due to the pressure from the typeface. This works for unused stamps with gum but not usually for used.

Thank you Germania.I don't have yet the stamps.It's a print-screen of a sell site.
What caught my attention is the number 1 from 1920 which has different heights.

The "9" looks different, too. I would need to see the actual stamps to be certain. The catalog does note that forgeries exist. On the other hand, the difference in catalog value between the original stamps and the overprinted stamps is not so great that it would seem worthwhile to forge the overprint.

But I will change my opinion and recommend not to purchase.

Thank you Germania.The 1 of 1930 is different too. But,who is the genuine overprint?(if is one)
I saw these stamps in floortrader's collection. If he sees my post he can confirm if there is a difference between the overprints on the 50 and 75 pfennig stamps.

I believe that is just a minor plate variety.

Thank you floortrader.I have 4 hours to the finish of auction.

Gerhard Schueler's Spezialkatalog der Danzig-Briefmarken lists two types of overprint forgeries for this series. Hope this helps.

1. zinc plate counterfeits, mostly on used stamps
a. "5" too clumsy
b. "v" shorter and higher than other letters
c. "r" not saddled up
d. "3" of 1930 too clumsy

2.lithograph printing forgery
a. "1" of 1920 too deep
b. head of "9" too thick
c. "r" not saddled up
d. neck of "5" in 15 too short.

Excuse me for delaying the answer (time difference)
I don't buy the stamps.
Thank you very much "bookbndrbob".You save my money.