By/under/on false pretences
Definition 1 of 1
Pro Tip 1/3Legal Context
This phrase is often used in legal settings where someone deceives others for personal gain. 
The company was charged with selling products by false pretences.
Pro Tip 2/3Negative Connotation
'By false pretences' implies dishonesty and can suggest a lack of trustworthiness. 
They worried she was courting them under false pretences.
Pro Tip 3/3Not Literal
The phrase can be used metaphorically to describe any situation involving deceit, not just legal or formal ones. 
He felt like his friend had invited him over on false pretences.