I do not know how it works, but a few times I have purchased Giants football tickets, on NFL.com/tickets All teams are on there.
I do not trust Craig's List for anything. It is a LOT of $$ for a pair of tickets, so I feel safer using the official site. I am not sure how they have tickets, I would guess season ticket holders have them sell them for them somehow? They are available all over the stadium, and the Giants are sold out.
In any case, you could look on there to see what your seats would sell for on there, and ask a little less I guess?