Sadly there is zero trust with police. Since testing for THC levels isn't an accurate measurement of impairment, I normally would say have a field test. However, I've seen my multiple examples just this week of police abusing this and trying to bring in people for DUI with no alcohol in their system. They can't be trusted to treat THC impairment without a physical test.

This is yet another reason why the police suck. We cannot have good laws because those with the power to enforce them, abuse that power immediately and constantly.