With stub hub its more legit in terms of you are certain these are real tickets.

You can also look on craigslist where someones plans changed or they cant go because of the game time change.

If your friend is local maybe they know of someone who cant go now because of game time change thus conflicting with a holiday party or travel plans....same reason you may find postings on craigslist.

Ebay is another place to search.

I dont recall if the seahawks have an avenue through there internal office that allows season ticket holders to resell tickets. I have seen such a system with NHL teams.