It's tough to get sell-outs to local fans when:
a ) A certain amount is alloted to visiting teams,
b ) The tour companies from opposing cities can get tickets before "Joe non-Season-Ticket-Holder" can
c ) Believe it or not there are people in the Buffalo area that are not Bills fans. A Bills fan has 8 chances to see the Bills a year, local fans of other teams have at most one chance/year, and in the worst cases once every 7 years or so...
There are not enough people in the area to sell 70,000 season tickets, so opposing fans in the stand will always be an issue. At the same time, how many games were effectively sold out before "Joe non-season-ticket holder" had a chance to buy? (Yeah, I know, buy through a Season Ticket holding friend...). Issue "b" is the only one the Bills can do anything about, if they chose to...