I'm interested in the Sigma 50 mm 1.4 Art lens.. every place has it listed for $950 but this Amazon one is listed for $190 cheaper. What gives? The seller is "Abe's Electronics Center" but seems to have good reviews:

https://www.amazon.com/Sigma-50mm-F1-4-Lens-Nikon/dp/B00ICJWP6S