You also understand that hitting and pitching instructors make at least part of their living teaching lessons. To me, we are like chiropractors. You always need to come back for adjustments. (sorry to any chiropractors but I tell my friends who do it the same.) Why would you teach it or fix it all in one visit when you can perfect it over time. I think hitting lessons have to be player specific. I know guys who can take bad hitters and make them good hitters but can't take good hitters and make them great hitters. Most of the MLB or college great guys cannot take a bad hitter and make them good. they are great with working with athletes but not so much with the lower level kid. You have to find the coach that fits best with your kid and his level of play.
My son has never had a hitting lesson from anyone other than myself, his brothers, and his coaches (which were pretty good). He hit .500 dead on last year in HS with 7 HRs and 28 walks with 19 of those being intentional.
I give hitting lessons. I am one of the guys who can help the younger players and the developing high school players. I do a decent job of teaching mechanics. I just don't always have the patience to deal with middle level high school players and their dads who say I've always hit this way and had success (which means batting .200 and never come close to hitting a HR on a big field) can't you just tweek it rather than me change it. I just got to the point where I say here is what you need to do and it is up to you and your kid to fix it if you want to get better. I find there are too many dads who were decent HS players who think the way their coach taught them back in the 80's is the way it has to be done.