Pretending like you don’t know someone

Scenario: you pretend like you don’t know someone when you actually do then you start a relationship with them to get more information on them to use against them.

Example: A man meets a woman and already knows her information about her because people have told him. He interacts with her then acts like he doesn’t know her when he actually does. After she finds out and is devastated that he only wanted to get close to her to gain more information to use against her.

Do you believe that this is a right thing to do or wrong thing to do?