New, this configuration would cost over $12K from HP. At about $7.5K this HP Z820 workstation with dual E5-2687W CPUs, 128GB RAM, liquid cooling and NVidia Quadro 6000, is a sweet deal. While the Quadro card is a bit old in the tooth, gobs of memory and fast processors still make it a terrific editing system.
(We don't know the seller and endorse neither them nor the product.)
To make it an editing system for, say, Adobe Premiere Pro CC: swap the graphics card fro Quadro K5000 or GeForce GTX-780 Ti; add internal or external storage; monitors.
As with any used or "open box" products, check the remaining warranty and seller's reputation before buying.