Never...You ever come out loser in this scenario? !!
However, I'm not greedy and I try to make it fair for the person taking a lesson. I enjoy playing pool, and growing up, no one taught me how to play. I learned by playing better players until they would not play me anymore. Happened every time
I am glad to pass on knowledge and have people grow their games and enjoy One Pocket more and more. Its nice to see someone getting better and attribute it to your guidance.
Some players don't teach as they want to limit their competition. They feel if they teach people, it makes it harder for them to win. This is bs as far as I'm concerned and I won't stop learning myself, so where is the harm in growing people around you?