Germany Office In China Stamp On Piece

My friend said this is a fake overprint but I think it is genuine. Any thoughts?
I would like to know more about this stamp such as Scott's # etc.
Also is it worth having the stamp certified?

It looks suspicious, but I think the authority on these is PostmasterGS. No doubt he will chime in.

https://www.germanstamps.net/imp-aus-chi/
https://www.germanstamps.net/imp-kol-kia/

It looks genuine to me.Tongku post office with provisional China ovpt. Some of these overprints are very messy looking..

IMO, very, very fake.

If it serves to clarify something about its validity, I put images with what the specialized Michel catalog indicates... This overprint of China diagonally on the Germania was issued for the Tientsin post office and the postmark is from the Tongku office. The value of the stamp, if it were authentic, its postmark is high, so I think it would be important to investigate something more... They are overprints from this era that in most cases are very precarious and I would not go ahead to give my opinion on their authenticity. .
Greetings

German Offices in China is a very new field for me. I learned a lot from everyone's comments.

Thank you very much.

Am I the only one that gets instantly suspicious when something is labeled "On Piece"?

A tattered cover is still better than "On Piece"

Maybe.

If you do not collect covers, but the cancellation makes the stamp valuable, 'on piece' is a very legitimate way to show the whole cancellation.