I agree that there are a lot of good CFI's, and a lot of bad ones.

When I was flight training, I had some of the best CFI's I had ever met (even up to this day). My private instructor taught me an important lesson that I later applied as a CFI. I was a college student who was paying for my entire flight training out of my own pockets, and I did not want to be overcharged! He did not charge me from the moment I walked in the door until the moment I left.
He would charge for two things:
Flight time
Meaningful ground instruction

An example:
I walk in the door at 2:00, call and get my weather briefing
We sit down at 2:05 for a discussion of what we will do on the flight,
At 2:20, we stop talking, and I get the keys to the aircraft and we walk out.
On the way out, we sometimes talk about about flying. Other times we would talk about sports teams. Sometimes I would go out by myself and preflight, while he finished up other business.
By 2:40, the preflight was done. We hoped in the airplane, took of and flew until about 3:45.
We walked back. I paid for the airplane while he signed my logbook. We would spend about another 15 minutes doing a postflight briefing.
4:15, we are done for the day.


Even though I was there for 2:15 minutes, what did we do?
15 minutes of pre-flight briefing
1:05 of flight time
5 minutes signing my logbook
15 minutes of post flight briefing.
For a total of 1:40. He would usually round that to 1.5.

I apply this same method to all my students. Why should they pay for my time when they are preflighting the aircraft, and I am just standing there. I would usually charge them for the first few times when they learn to preflight (because I need to teach them and then watch over them carefully). But after we have done a few flights, there is no need for me. I am just killing time. Same goes with the walk to/from the aircraft. No need to charge if we are BS'ing about how nice the weather is, or what we did over the weekend.

As far as I am concerned, the only time I will charge for is either:
a) in the aircraft
b) when I am actually teaching them something (i.e. I am talking)

As a student, I once had an instructor who would charge me for preflighting while he sat inside. After I questioned him about it once, I told him I want him to either be outside teaching me something useful, or he could sit inside and not charge me. But if he continued to charge me for nothing, I would no longer fly with him. Problem fixed! I believe flight instructors should charge for time when they are "teaching."