Thanks for your post.
Did you already see this Knowledge Base article about How can I restrict access for TeamViewer connections to my computer?
The chapter about Restrict features for incoming connections might be relevant for you.
Hope this helps you.
It's the other way round.
I want to restrict my staff to provide TV support for a customer computer that it's not paying service agreement.
what about adding a whitelist to the devices of your staff members and add the customers they are allowed support?