What is the official way (if there is any) to deal with people who commit reputation fraud? With that I mean following behavior:
Posting of abbreviated version of old answers, to gain reputation. Possibly involving 3rd party to up-vote them.
Re-hashing of old answers requires attribution, in accordance with the CC:Wiki license used on Stack Overflow. In other words, the poster must:
Failure to do so gives the impression that the poster wrote the answer himself, and people do vote accordingly.
Copying other people's answers without attribution is a suspendable offense, and so is sock-puppeting. Cast a moderator flag on one or more of the offending posts, with a custom description explaining the problem, and a moderator will take care of it.