I think Sam is not as "good" as we think he is. He enjoyed killing Sookies uncle. He has already lead Sookie to believe that he doesn't drink human blood anymore. When/If she finds out that the same teeth that were/are in her neck had been in molsting uncles she will flip.

Did you hear the guy in the bar mention there was a "full moon" that night. It happened after the bar fight as they were closing that scence and moving to another. You only hear it being said.

If Sam isn't a werewolf after all of this it will be a "bite" on the stupid side.