I . Mine will "double" (ie fire both barrels) if the rear trigger is pulled first -
This of course is completely unsatisfactory but endemic on Merkels. You should send it back to them for repair. As to the prospective buyer:
1. I would not own a double unless it was a rimmed cartridge
2. I wouldn't own a Merkel unless I could steal it and 8K is WAY overpriced for a used Merkel and in that caliber.
3. I wouldn't own a Merkel for personal use on a dare.