Aside from network warnings shown on a user's video window, checking the network stats is helpful to identify the cause why you may be having audio and/or video quality issues.
Please take a screenshot of your stats and include it in your email when you contact email@example.com
1. Windows: Press "Ctrl" + "I". Alternatively you can go to your address book and click Settings > Network Statistics.
Mac: Go to Window > Statistics
Android and iOS: Click More (...) > Statistics
2. Under Users tab, you can view any user's network stats.