Free uninterrupted competition will destroy people/companies overpricing their services or force them to compete as well => lower their prices. Basically, offering poor/expensive service in capitalist system will naturally invite competition until the optimal price/value point has been reached.
But like I said, that works in pure free market capitalism, which no politician would ever want to try because it would take power from them and give it to the people and markets.
If all the farmers form a cartel, where does this mythical competitor come from? Farmland is a limited resource. And food doesn't just magically appear the day you start a new farm.
I am pretty sure that teaching and medicine are the kind of good that would break these rules - political implementation, people and markets or no.
The value of your teachers (or lack of value) will only become apparent over time - a long time. The value of your doctor may become absolute to you, several times over your life. God forbid that you or yours fall sick, but should your doctor be able to demand all of your worldly goods to heal you? What about farmers - should they gang together and refuse to supply food until starvation set in would that allow them to demand all of the cities wealth? If no then what is needed - is it a rule of law that enforces particular norms of behaviour?