Hard to win in the preseason, all these games are coin flips, no right way to handicap them... you never know what you are going to get with so many players playing, coaches trying new offense and defense schemes, players trying to adjust to new teams, coming off injuries, and players adjusting to the NFL level of play, and much much more.
That's why I stay away, I learned my lesson before. All I do now is just watch the games intently and study whats going on heading into the regular season, there is a lot to learn during the preseason. I might bet a couple dollars every now and then, just for the fun of it... but that's it. You cant take betting on the pre-season seriously.
But as I said, its a coin flip... and the odds just evened out against you towards the end.
But good luck heading into the regular season!