Being a billhook collector, this is obviously a late 19th, early 20th century billhook, and I would say very likely French. Germany doesn't have a great tradition of billhooks, and I may be wrong, but I've never seen one with a socket like this made to be mounted on a pole. These, with the large hook in the back, are specifically designed for debranching: you chop the branch, and the hook is used to catch the branch and bring it down if it is stuck.
I don't have that very exact pattern in my catalogues, but these two come pretty close. From the Revolier catalogue from around the 20's I scanned and is available on the internet
, and see Bob Burgess website
for more catalogues. But unlike hand-held billhooks, these pole billhooks don't have a strong local identity and recognizable traits. And basically, the same kind of tool could also be found in Italy, Spain or Portugal. Maybe Germany also, but that would be unusual.
Estimated value: no more than 30€. 10€ is more like it. If you friend paid for this as a 17th century Scottish bill, he got screwed big big time.