The victim of the alleged boat theft noticed his stolen boat for sale on the popular buy-and-sell website Blocket.se, and decided to pay the seller a visit, Sveriges Radio (SR) reports.
Accompanied with five friends, the man got into a heated discussion with the suspected boat thief, proceeding to hit the seller in the face.
The original owner and his friends then left with the boat, as well as another boat with the original boat's motor.
The prosecutor didn't believe that the boat really belonged to the man and charged the six men with robbery.
But the Värmland district court was of another opinion and found the man and his five companions guilty of taking the law into their own hands (egenmäktigt förfarande).
The original boat owner was also found guilty of assault and all six were sentenced to community service.
The boat seller is set to receive damages of 20,000 kronor ($2,500), but the boat will remain in the possession of the original owner.
The court did not find that the seller purchased it in good faith.