How to set prices for works on semantics?

Question

Search Engine Optimization

Good afternoon.
Tell me, how best to set prices for work on semantics? Two problems:
1. In freelancing (and not only), the price usually needs to be announced in advance, but for most topics it is impossible to predict how many keywords will turn out and how long it will take to clean.
2. Even if the semantics has already been collected and the number of keys is known exactly, it is impossible to predict how many of them will suit the client and it can easily turn out that he will filter out half of them.

Actually, the question is, how do you solve such problems? How to arrange pricing in order to avoid conflicts and misunderstandings as much as possible?

Answer 1

If you are selling your work and not the result, then simply accept payment for the hours worked, and at the entrance to the client give a plug of hours for work