If there are complaints about the AT Max, it’s likely due to noise and erratic behavior. There are few things you can try from ensuring the connection to the control box is tight, the searchcoil is correctly installed, and the coil wire around the shaft is adequately tight and not loose. You can also replace the searchcoil with a new one, replace the batteries, and hit the factory reset button. As far as settings on the detector go, ensure Iron Audio is off, change frequency, ground balance, and discrimination settings. You may even have to go as far as reducing sensitivity if erratic behavior is caused by excessive metallic trash, nearby metal detectors, electrical interference, and highly mineralized soils.
The AT Max comes with a 2-year warranty, so be diligent in registering your detector with the brand for warranty claims or replacements. There are also many advanced tip videos online specifically for the AT Max.