I work in a support role for one of our products. We have B2B customers and frequently they will contact me with issues. When a request comes in, I let them know I'm troubleshooting and will give them an update soon. Many times, the customers will then subsequently send a meeting notice to me. Sometimes when I join, the issue is fixed and other times it's not. When it's fixed the meeting is really just "what can we do it prevent this in the future", which is a fine question.
The problem is that when it's not fixed yet, I'm starting to be asked to troubleshoot and fix it in real-time. I literally had a customer ask me to share my screen (when I was on their network) and ask me step-by-step what I would try next. Because it's a customer I feel like I can't say no. And I have a very hard time working when someone is right over my shoulder judging my every move. It makes me feel incompetent when I don't know something even though I've been doing this job for years.
How can I ask the customer to give me some space in a polite manner?