One thing I've learned about collecting German Colonies is to never write-off any card or stamp as worthless or of minimal value without doing my homework. There were many small post office scattered through remote areas of the Pacific and Africa, some of which were only in existence for days or weeks. Cancels for some of these are extremely rare.
Consider these (and no, I can't claim ownership!)
Two identical stamps -- German New Guinea Michel 9.
The first was canceled at Rabaul, and the second at nearby Buka about 11 days prior.
The first can be had on eBay
for about €5. The second is only seen at auction about every 10-15 years -- most recent I know of was at Vogenbeck Auktion about 10 years ago. Final hammer price -- €11,250.