If all of the mags are factory mags, then I would say that it's an OK deal.
The gun is around $500 NIB with the night sights, so you are getting 3 extra mags (used) and a used gun for $30 more. I would try to talk the seller down a little. $485 - $500 sounds like a better DEAL. I know that it's only $30, but that's 2 boxes of 100 round Winchester Value Packs.