All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Having no relationship with the one who does something wrong does not prevent from denouncing his evil deeds; however, this should be done with wisdom and good instruction. So, if that person rejects advice and refuses except to wrong people and consume their wealth unjustly, then he should be threatened with informing the authorities if he insists on doing that. If this was not effective and one can inform the authorities with the bad things he or others do without causing greater evil than that, then it is obligatory to inform them to save the rights of the people by those who have power to do so. However, the resulting benefits and harms should be taken into consideration.
Scholars have pointed out the degrees of changing evil according to its consequences. So, it has four degrees:
Firstly, if denouncing it will remove it totally, in the sense that good will follow and no harm will result, then it is obligatory to change it.
Secondly, if denouncing it will lessen it, although it may not be removed completely, then it is also obligatory to change it.
Thirdly, if denouncing and changing it will remove it; however, evil of the same degree will follow, then one should use his personal diligence to decide the most appropriate course of action.
Fourthly, if denouncing and changing it will remove it, but greater harm and evil will follow, then it is prohibited to be changed or denounced.
What you asked about, i.e. informing the authorities, is most likely included in the last impermissible kind that may cause disadvantages which outweigh (the benefit of) changing such evil. So, you should only advise, instruct and explain the prohibition of cheating and deception and the bad end of those who do that as we have explained in Fataawa 87677 and 131330.
Allaah Knows best.