Most people purchase scopes then trade-in as they trade-up the equipment tree. To facilitate this, there has to be a market for second hand equipment.
I have purchased Celestron and William Optics over the years and was after a starter scope for my son, so bought an Orion Dobsonian off ebay, from someone trading up. (Note this is Orion US , and not Orion Optics UK)
The courier managed to damage the scope, so ...