Who verifies the position of the site for signing the act of completed work with promoters?

Question

Yandex

There is an office that promotes the site. At the end of the month, you need to pay a certain amount in accordance with the positions of the site. But we have an eternal dispute how to check the accuracy of the position of the site? Our search engine gives out one position, the company of promoters reports completely different positions.
How do you proceed in this case?

Answer 1

agree in advance in the contract the criteria and methods of verification

Answer 2

I communicate with promoters why the positions are different.

Answer 3

Do you turn off personal searches? Are you using incognito mode?
What is the point of promoting by positions now, when all search engines have personal search enabled, and the results are different for different people?