Longer serving members may have heard this anecdote before; bear with me as the OP is a new member.
Our club had a member with a Logun S16; the member lent the rifle to his brother. They were both aged in their late 20's and were entitled to possess an air rifle.
The brother lived with his girlfriend at her mother's house. The mother didn't take to him much and she called the police and said he was being aggressive and "had a gun". The police arrived and took him into custody and seized the rifle, for testing.
When tested it was found to be capable of 12.4 fpe.
The police contacted the dealer who had sold it and he called me to ask if the club had any chrono records of this gun; naturally he wanted to make sure he was off the hook. We didn't have; if we had had, I doubt if we would have divulged any info.
The owner asked for his gun back; the police refused as he didn't have a ticket. They wanted to destroy it. We at the club were able to show that the owner was of good character and was not the kind of person to knowingly own a hot rifle, and was manifestly not the type to "tune it up". He had neither the inclination nor the knowledge.
Eventually the police agreed to let the original dealer send the rifle to Logun to be turned down, which he did. Once the rifle was certified as under 12 fpe the owner could have it back. In fact the owner no longer trusted the rifle to remain legal and he negotiated with the dealer to trade it in for something else.
The dealer then sold the Logun to a new purchaser. I recall suggesting to the dealer that he should make the new owner aware of the gun's provenance, that the police probably held the serial number, but I got the impression he didn't intend to. He has since gone out of business.