In the data related blunder to hit the UK, a laptop that has been sold on Ebay happened to contain data from the Home Office which was fortunately encrypted.
The world's biggest auction site sells hundreds of thousands of laptops, desktops and storage devices and peripherals every year and it is highly possible that a fraction of these contain sensitive information that can be retrieved.
There is a large number of refurbished hard disk drives on Ebay which means that they have been removed from a working machine and wiped clean.
Wiping clean a hard drive however requires more than simply formatting it; there are a number of Professional data recovery firms out there and there are applications like GetDataBack for NTFS, Active Undelete, or Recovermyfiles which can be used to undelete files from low-level formatted hard drive.
Drives sold as faulty could potentially be hiding valuable data for criminals and are the ones which will go for cheap because of their state; furthermore, because they are broken, they can't be wiped clean.
SCSI hard disk drives are also likely to have contained business or corporate data at some point as this technology is historically quite expensive and unlikely to have been used by consumers; they will also go for cheap because of growing obsolescence.
Companies should where possible get their hard disks decommission professionally, albeit at a cost, rather than selling them on Ebay.