This is an OEM BMW accessory. Part number 82710302450 .
In great condition, some small superficial scratches but nothing out of the ordinary. It includes everything that comes from the dealer, except for the instructions (honestly, you don't really need them) and the adjustment/rail knobs for the back support beam.
Because of the way this is situated, you actually don't need these back rail knobs -- the front ones are the only ones necessary. The back horizontal rail is physically limited in lateral movement by the sides of the car trunk. They also make adjusting the bike rack harder if you're putting in two bikes (which is already a tight fit). You're honestly better off without them -- and the bikes are firmly in there without them.
$255 at Circle BMW. Selling for $130 + $20 shipping (they're a bit bulky, hence the higher shipping cost).