May I suggest that on your ticket form you have a tick box for "Support Access Granted".
I almost always have my support access granted, but occasionally I forget to mention it. Then we waste time with the tech writing back to ask me to grant permission. Then I have to wait again for the issue to be dealt with.
If you had a tick box, it would be a reminder when we need to turn that feature on, if we haven't done so already. It would be a time saver for your techs and your clients.