Organization of payment on departure?

Question

Computer networks

We have IP USN 6%. Maintenance of computers and infrastructure jur. persons. For payment, everything is clear, current account, bank transfer.
Entering the physical market persons. Only home visits. How to organize payment for work in this case? Of course legal.
Much has been read, but the ultimate goal has not been achieved.
Are there people who already do this? Reach out and share)

Answer 1

I see the conclusion of an agreement as the only correct solution, in which the main provisions are spelled out, and the details are already in the appendices to it. Lawyers will tell you the details, I think.
It may seem hemorrhoids, but for that it is legal.

Answer 2

The check can be printed in the office and delivered by courier while the engineer is doing the work.
(all the same, before the work, you will have to name the full cost - few people agreed to carry out work in the spirit of "I'll do it, and then we'll calculate it").