Good price for a used 3rd party Nikon lens?

F2.8?

check bhphoto.com, also what is the fstop?

Yes it is f2.8. (http://www.sigma-photo.com/lenses/lenses_all_details.asp?id=3253&navigator=5)

I’m not a Sigma fan to start, you’re better off spending a bit more for a Tokina or Tamron in my opinion.
Is there any substantial type of warranty associated with this purchase? Are you guaranteed to get your money back if it’s a piece of junk? Is it a local seller so you could go try it out before purchase?
I’d be very careful buying anything that did not carry any protection for the buyer.
Do you ebay,great place for lens, lot of good quality retailers with used equipment and waranties, plus pay with paypal most times and you have 100% money back if not as advertised.
Good reviews, about $400 anywhere, for a lens this new $350 is a good price.

I agree with @pekenoe, besides buying first-party lenses, I’ve had better luck with Tamron lenses than Sigma, and if the savings is only $40, go ahead a buy a new one that has a warranty or used as long as you have protection just in case.

Not a Sigma fan at all. Your lens is everything, so you might as well get the best you can for your money. Zeiss, Nikon are top choices.

I fourth that opinion.