I have a friend who buys a decent amount of tix - aftermarket - for all Boston teams to give away to his customers. He wants to buy mine, but I would never think of selling them, even for face as I would worry about someone misbehaving in my seats...hell, I don't even give any extra's away to anyone but my own family and they are warned to be on their best behavior!!
With Ebay, be certain the seller has excellent feedback and is local.
I asked him about this and he told me to try to stay with hard tickets as opposed to the Ticketmaster "E" tickets. The only way hard tickets will cause a problem is if they have been stolen and reported stolen. "E" tickets can be printed out multiple times and the first person to enter the stadium will be the only one to get in as once used, the barcode is then voided. That actually happened to this guy and it was embarrassing to say the least. he had bought tix through Stub Hub and the customers he had given them too called him to say they were denied!!. Luckily, they were able to buy some just before kick off from some that were released. He said Stub Hub gave him a refund but he damn near lost a big account!!
Stub Hub tends to be priced very high and there is a little war between the Patriots & Stub Hub going on, so he says to shop around and maybe avoid them totally.
Consider going 100% above board by doing the Tailgate experience of Fred Smerlas - Twin River tailgate or something like that. It is pricey ($625) but it's an awesome all you can eat 3 hour pre game and a nice 2 hour post game, with a ticket in lower bowl or 200's.
Also, look into auctions from WEEI or even the NFL.
The popularity of Pats tickets simply amazes me as I still recall, not too long ago, that at most 23,000 would attend a Pats game on any given Sunday!! No lines coming in, no bathroom delays (even in those horrible and inadequate rest rooms) and no traffic leaving at all. There used to be two kinds of football, football the way the Pats played (weird and unlike anything else in the NFL) and the way games were played everywhere else...normal football, real football, not football twilight zone style.
GOOD LUCK!