I usually buy on StubHub because I used to have to drive a distance and didn't want to take a chance.
I was headed to the ND-UGA game last year and prices kicked off at $400 for bad seats and folks said I should wait. They went to $700+, so I ended up watching on TV. ND seems to attract high prices, and Dawg fans were snapping up anything available for that one.
Now I can "afford" to drive to Athens and take a shot with the local vendors. If I don't snag something I can walk to a bar nearby and do OK.
I may go to a GT game and I figure there would be no problem unless they were hosting a Clemson/FSU/UGA kind of opponent, maybe VT.
Stubhub has been reliable in my experience, though expensive of course. I got tickets to a UGA game at Ole Miss on the 40 for not much a couple years ago, something like $125 a piece. The game did not sell out. That surprised me.