Generally it is a good idea to keep to the latest version of a software. A quick search on the exploit database reveals several vulnerabilities for team viewer, including a dll injection exploit that allows an attacker to override or ignore the permissions of your server with his client with team viewer version 13.
I am not sure if both client and server have to use version 13 or if it is enough for the attacker to be using that version.
Either way it is a good idea to only give your access information to people you trust. Even if there weren't such an exploit in the software itself, some expert could easily do something you don't understand with some powershell script running on your computer while opening a session in the background, or install some vulnerable service that he says you need or whatever.
All that's needed is to open a prompt, pasting whatever exploit/payload and then hitting enter and closing/minimizing the CLI and disguise it as some normal workflow.
Generally speaking you should be safe if you pay a trusted and reputable company to fix your problem. Keep your software updated and don't give anyone the data they need to access your machine. Or in other words have the brain.exe service always running.