Upload & Sell: Off
The is pretty tellingreview by dmdinius on reseller ratings. Even if you assume that was planted (which may sometimes be the case), the overstockdigital's response to this negative review clinches it! If you follow lens prices at all, you'd know the fair price for that Sigma (there're ways to find that out), and you'd also know that Sigma's longer warranty is also standard and comes at no additional cost!
Huge red flag!
p.s. Okay, the longer (7-year) warranty for Sigma lenses seems to be available in Canada, not in the States. Still, the price is outrageous, as is their explanation.