One thing to consider is that some people don't understand how to treat a radio. They'll often use the antenna as a handle, beat the snot out of it, etc. On some radios, not sure about these, it's common for the antenna mount to become separated from the circuit board. Result is that the radio works poorly.
Not saying it's the cause, but I've seen a lot of radios with this issue. No matter how many times you tell people to be careful with the radio, they still treat it like crap.
I also had a radio once that the amplifier transistor was toast. The radio put out about 30 milliwatts when keyed up. This one was brand new, so it was a factory issue. Sometimes a damaged or missing antenna can do this, or someone using a UHF antenna on a VHF radio, and vice/versa.
I agree with Cabletech, they probably need to be looked at closely.