I learned this lesson recently in a small weekly tournament. Hit a shot and cue ball didn't do what I expected after a kiss and was heading towards the side pocket. I thought it was 100% a scratch, it should have been and I had my hand in the pocket waiting to catch it. But it stopped, it hit some little piece of chalk or something and held up just at the very edge of the pocket and even rolled back a tiny bit. I was shocked but hadn't touched anything and just kept shooting. When I got back to my chair my opponent, who had much more tournament experience than I, said I should keep my hands out of the pocket just for cases like that as there are many people who could try to call that a foul thinking I interfered with the shot.
It was a good lesson, let things happen on the table as they're gonna happen and stay out of the way. It's not a long walk to the other end of the table if it's a ball return.