Reminds me of my return to flying a few years ago now. I was with my new instructor, we ended the first lesson, I paid, then I thought of a few more questions. I kept him about another 30 minutes, I noticed he was giving me a weird look every once in a while, but he was very polite and answered every question. I got home and thought about it, then realized he was teaching me and not being paid for it. So next lesson, I told him that I should've asked my questions while he was on the clock last time. I said that it would probably happen again and I understand this is his living, I didn't want him working for free, so I told him to add the extra time to the next lesson when I do that. It happened a few more times and I paid him for it, everyone was happy.