I shoot the bastards. That's my policy!

Shoot first, ask questions later.

The rules that apply to work as an informant vary depending on the jurisdiction and the police agency, but throughout the U.S. these are some of the common rules that apply for informants:

Keep in Contact with Police: It is important that an informant can be reached by the police. If an informant disappear and can't be reached it will often be assumed that the person is up to no good.

Don't Act Without Authority: An informant cannot go on his own assignments and investigate people and make buys without the supervision and knowledge of his supervising detectives.

If an informant goes to buy drugs from someone with the police supervision, it will be assumed that he is planning on using the drugs or reselling them.

Don't Use Drugs: Generally a contract for work as an informant contains a provision prohibiting the use of illegal drugs. However, if an informant is in a situation where he will cast suspicion upon himself by not using, it is common for law enforcement to look the other way.
Sometimes the informant agreement contains a provision for random drug tests but this is not commonly enforced.

No Possession of Weapons: Although an informant will often want to carry a weapon for protection when working as an informant, informant contracts usually prohibit weapon possession because it is too much of a liability for the police agency.

Tell the Truth: Whether an informant is working with the detectives or testifying in court, he or she is contractually obligated to be truthful. Defense lawyers often question the sincerity of drug informants.

Confidentiality: The contract informants sign provide that they cannot tell anyone that they are working as an informant. The means they cannot tell their spouse or their parent. In my experience when an informant makes an exception, and tells his father (for example), the father in turn will tell the grandmother, who will tell her neighbor, and then the whole town knows. The police really try to avoid this because it not only blows the case and waste agency time, but it puts people's lives in danger.

Police Academy Playlist
https://www.youtube.com/watch?v=zV7BUYnALIo&list=PL-j-DijYQ2A9dOTDJOxHHBkChehl_-3Tb