Well the stories abound about returned goods resold as new- particularly one electronics vendor. Whole PCs which when started reported to be registered to another person or eve containing data.-This story has seemed to have faded of late- so perhaps that firm has got the message.
But as a former Mail House worker of many yonks ago[specialist medical supplies] returned goods were processed and restocked/sold off in bulk or plain 'dumped' according to condition and nature of the item.
And I suspect it is true to-day in the mail order industry. Simple incorrect ordering/supply- then items would be restocked.
Item returned deficient on inspection- restocked and sold at discount or put in the bargain basement section.
But I guess it is only humans doing the work and inconsistencies are bound to crop up.