Low Quality in Nero test is due to bad media or bad burner ?

Thanks

It's hard to say unless you can provide us what media, MID, burner model, firmware used, burn speed, and the quailty scan. Also here in this forum we are used to see "excellent" burn quality so sometimes a burn nicely within specs is suggested as bad result.

Anyway, I believe most of the time many problems here are due to low quality media. However there are some instances that a well respected media brand does not like to be burned at the highest possible speed in certain burners and this is due to a combination of media variability and firmware support, among other things. This is why many models are equipped with AutoStrategy, SolidBurn, SmartBurn or similar methods to handle media variability and low quality media (but not always work).