+1 on the volume/on/off pot issues, as well as some build quality problems on the PTT button bezel (you have to recase the radio when that breaks, which is common). This is the case for all of the APX line though, PTT button bezels tend to crack, and like similar constructed XPR radios (XPR7550/e for example), a new case is needed, or some super glue can help until a new case is available or needed.
APX900's are decent radios but they lack the dual microphones of the higher model APX4000, so they are good if the end user is NOT in a high noise environment. For forklift drivers, machinists, or any users in high noise areas (HVAC, possibly firefighters with pumps and water spraying around) I would highly recommend the APX4000 instead.