The Gift Economy.
I am a firm believer of the Gift Economy. I use it in all my work.
It is based on mutual trust. It means that you trust that I give to you my knowledge and wisdom to the best of my abilities. I trust that you appreciate me by giving me the true value it represents to you. The way it works practically is that I will give you a proposed value of the work we agree to undertake together.
I trust you value me in the appropriate way.