To buy a used computer you need to be careful to see if the machine has been disassembled. This is mainly used in laptops. You need to look carefully at the back of the laptop those screws, there are not a lot of are screwed traces, if so, then the other side still insist on no disassembly and no repair is very problematic.
Open and close the screen a few times, to see if there is a clear sense of looseness, if there is a greater sense of looseness, the spindle is worn out more, the screen may not be fixed in the position you want, in addition to wear and tear after the spindle will also have a negative impact on the screen wiring.