Project TinyMiniMicro
If you purchase one of these units, especially second-hand, you may end up with a great deal, but there can be disasters as well. For example, one of the HP models arrived and it was a similar yet different model. Some were missing parts as well. Others had very interesting default BIOS settings.
This is actually something to look out for. When I bought the Optiplex 7020 SFF it came with a 9020 sff front bezel. Motherboard, BIOS, all checks, confirm it's a 7020 sff except for the front bezel. It seems to be a factor of who is actually doing the 'refurbishing'. If it's someone official, you probably won't have any issues, but if the reseller is the one doing the 'refubrishing' it can get piecemeal.