In every case, an officer's actions must be reasonable, meaning other reasonable people in similar circumstances would draw a similar inference. A police officer cannot simply say I "thought" that car was parked illegally; he or she must describe observations that would lead a reasonable person to believe the car was parked illegally.
Another clause missed by most of the bill's opponents is this, the second-to-last sentence of the act: "This act shall be implemented in a manner consistent with federal laws regulating immigration, protecting the civil rights of all persons and respecting the privileges and immunities of United States citizens."
Let me repeat the key phrase: "protecting the civil rights of all persons...." Please bear that in mind when debating the relative merits of this bill.