in Murder Under Glass he switched up the wine glasses. Just as the killer was about to take a sip Columbo said no, I wouldn't do that sir. Something to that effect.

The second part of your post is very interesting. It's true you never see anybody get shot in that series by the police. As a matter of fact, there's one episode where Columbo looks completely lost when he's holding a pistol. I forget exactly which one that was. There was also another episode where he had to have his Sergeant qualify for him, I think it was in forgotten lady, because he could not hit the target

In one of the newer episode when Columbo was undercover, didn't he pull a gun on Burt Young in the hotel room?