Am I allowed to use "Quick Assist" as a self-employed user support technician?

phimo 

Firstly, you have to follow law in our country, in some countries even as freelancer, you have to register and get license.

You are not allowed to represent other company but you could work as your own and in this case, you may use any legal tools including Quick Assist. Many people use it to help someone else. However, you will need to be transparent like tell them you are seeing their screens and privacy concerns and make sure you have permission to access their device and explain troubleshooting steps.

Good luck with your support.