I never understood this kind of field work when officers propose using prostitution/drugs/you-name-it services. It looks like a crime promotion: person might he

I never understood this kind of field work when officers propose using prostitution/drugs/you-name-it services. It looks like a crime promotion: person might hesitate and never do a bad thing in years or they might do, but officers do help in it. It's almost like a prison for thoughtcrime. How do you know the crime would happen if the person weren't helped(sic!)