I used to play racquetball with my friend, Will, at the local gym. He didn't know how to play at all but I taught him how to stand and how to hit the ball with some basic strategy. Later, he took a class at the college and got better.
We played four or five games each time and I won them all handily. I never let him win, or let him off the hook. He got good enough that we were both fully exhausted by the time we finished. The game scores were closer and closer, 15-11, 15-12, etc...
Then, finally one day, on our final game of the day, Will won - 15-13. He was serving and I tried to pass him on the left side but my ball skipped; game over! He turned and had that huge grin on his face. He asked me if I let him win and I told him that he knew me better than that!
Later, he says it was an accident.