There's lots of reasons for selling used radios, and sometimes it's just because people want out of the hobby or someone acquires an estate from a silent key and has no use for the stuff, still others horse trade all the time like I used too...
But I agree... For the most part unless you can lay your hands on it and check it out good before hand, your better off to go new, than if something happens, off to the factory it goes for a free fix.