I think even if police suspect somebody, they should still treat them with respect, though. That is the real issue.
You can not ask the police to never suspect anybody - that would make their jobs impossible and ridiculous.
Here in Berlin we have parks taken over by drug dealers and people don't feel safe. What is the solution? I don't know. Berlin's government responded by giving the drug dealers designated areas for drug dealing. I rather suspect they rely on those dealers for their personal supplies.
That changed when the police started driving their massive SUVs on the park path after 11pm to make sure nobody was in the park. The first time they did it, they argued that the park was closed, though there were no signs saying the park was closed. It turned into a big verbal argument but thankfully it didn't escalate badly. That night I looked up the city code and found that if there's no gate, then the law allows me to walk to the end of the park. I went to the police station to complain, and was told that I shouldn't worry about it because they're not trying to get "people like me".
But still, it happened again, and the cop basically told me "we're going to keep doing this until you stop". So, while the cop wasn't exactly disrespectful, he was wrong about the law in a way that manifested no differently from persistent harassment. They're just trolling for anything illegal on a default position of wronghood.
You're asking the wrong questions.