During the performance. Write a note about the agreement will be made per hand or exchanging hands, or by email, as valuable as possible to remove all the evidence for official use.
At the Practice Writing notes about the deal being made. Or hand-to-hand exchange or email them. Are the values that can be taken as evidence for a formal.
During working. Write notes about the agreement will be made. Or the exchange of hand to hand or by email. All valuable can remove the evidence for official.