Open ear design lets the user stay aware of their surroundings without removing ear clips. So, user should not compare it with the earbuds.

a)  After all the probing questions, please ask customer to keep speaker close to ears

b) Make sure the volume is adjusted from all possible options. Like- Music streaming APP/Video APP/Mobile Phone and OWS

c) Use the device with different mobile phones and check if a particular song or video has the issue

d) In case there is low sound during call, then there might be network issue or other side user's mobile phone or BT device might have the issue

e) Try to reproduce the issue with different Mobile phones and different APPs.