From nolo.com, which looks to be a legal cheatsheet of sorts.

Case Example 1. Mary-Anne Berry is charged with selling illegal drugs to an undercover police officer. Berry testifies that the drugs were for her personal use and that the reason she sold some to the officer is that at a party, the officer falsely said that she wanted some drugs for her mom, who was in a lot of pain. According to Berry, the officer even assured Berry that she wasn't a cop and wasn't setting Berry up. The police officer's actions do not amount to entrapment. Police officers are allowed to tell lies. The officer gave Berry an opportunity to break the law, but the officer did not engage in extreme or overbearing behavior.

Case Example 2. Mary-Anne Berry is charged with selling illegal drugs to an undercover police officer. Berry testifies that, "The drugs were for my personal use. For nearly two weeks, the undercover officer stopped by my apartment and pleaded with me to sell her some of my stash because her mom was extremely sick and needed the drugs for pain relief. I kept refusing. When the officer told me that the drugs would allow her mom to be comfortable for the few days she had left to live, I broke down and sold her some drugs. She immediately arrested me." The undercover agent's repeated entreaties and lies are sufficiently extreme to constitute entrapment and result in a not guilty verdict.