In my 20s, I was taught by June Hager Walter not to give ANY ball to my opponents.
Even if they are straight-in on the 9-ball (or 8-ball if I'm competing in 8-ball), I don't give it to them and make my opponent shoot the shot.
So, I've kept that philosophy for the last 20 or so years. I just don't give balls to anyone. At anytime. No matter what during competition, I just wont do it.
And, a few times, that straight-in shot was missed, or they miscued, or they got impatient and missed.
The problem arrives when my opponent is giving me the 9-ball.
This happened in my match on Sunday on the Omega Billiards Tour (where I AGAIN placed 17th out of 80 players and took down that Last Lady prize of $75!).
My opponent was kind and when I had a straight-in, easy 9-ball shot, he gave me the ball/game. But later on when he had an easy shot in front of him, I did not return the favor.
While I felt kinda bad, it was no reflection of him, but just something I was taught and therefore live by.
But, it did cross my mind if he wondered why I didn't give him easy 9-balls, and I felt kinda bad for it. But, I stayed with my philosophy for the entire match. I know it's common courtesy to return the favor, but it's not a "rule."