A computer unit sold as "working" should have all critical parts inside
imo. If not, the description should mention what is missing. The seller
acknowledges that the FDD and HDD aren't there but completely ignores
that the entire processor complex is missing and that there is no memory
either (ignoring the other non-critical parts). If the seller can't test
the unit properly, they shouldn't be selling it as "working".
To your CPU analogy... If you are selling a processor as "working", it
should be complete (i.e. no missing non-redundant pins) and be in a
condition good enough to at least make it through the POST. Of course
you don't expect it to come with a motherboard if the item sold is just
a CPU. Equally, I don't expect this Model 90 to come with peripherals
like the power cord, keyboard and monitor...
But at least this seller has some good photos there - so a person
knowledgeable about these systems can figure out what is missing.