It's all about the CD transport
However, buyers of second-hand CD players have to be aware of the major source of potential problems - the transport.
There are several factors to consider - some transports are no longer made, some are not reliable and some are difficult to find, even from foreign sellers.
Being a moving part, the transport is always the first component to fail - the laser does not read anymore or the tray cannot open or the laser skips.
If you google around, you will find that there is a huge market for old transports. Many of them are on sale on e-bay; some are New Old Stock while others are reconditioned or cannibalised parts from old machines. There are also rumours that there are so-called "OEM" transports being made in China.
The problem with buying from an overseas seller is that there is no compensation when the transport does not work - and more often than not the transport will not work.
Recently, I was attracted to an old Esoteric CD transport and the seller was honest enough to say that the laser seemed a bit weak.
So I googled and found that the transport was a Sony KSS-151A which was widely used in several top-end marques at that time. Sadly, it is out of production.
Some experts are now advising that if you buy a used CD player which uses a transport that is no longer manufactured, you should buy a spare transport (or laser) just in case. This is a must if you buy a second-hand high-end player using top-quality transports such as the CDM-9 Pro otherwise the expensive machine will end up as another decorative item in your house should it stop reading CDs.