i had a guy back out on a sale on stubhub for stanley cup tickets. given the plethora of tickets for sale, they went and got me better tickets and it was sorted out with ease. the only case where i think the 1% fail with SH could happen, i think it would be lower than that, is in a situation where there is very very limited other resale tickets. i mean, even if you buy a 300 level seat, if the ticket does not work 2 hours out when the gates open, you still have more than enough time to call SH and i suspect there will ALWAYS be some stellar seats for them to buy on the other sellers dime and get you the same.
so i would say SH is about 99.9% safe....TE 100%.
[I will also add that this appears to be the most tickets I have seen for sale for a seahawks game on SH and prices are actually below what they box office was selling the limited tix they released...i would say in this case, buying through SH is pretty much a lock]