Arresting officers literally have a checklist that they use to fill out their reports. They try to hit every bullet point they can, and they tend to trump up charges. This is why the reports always sound identical -- because "slurring" and "staggering" are terms recognized within law.
Consider that many cops were once soldiers, who honed their skills in Iraq -- utilizing basic Fascist tactics and protocols, like occupying people's homes, holding without cause, and warrant-less searches. I trust the police to be honest no more than I trust an employee of Best Buy to be honest...actually, less.