This is a very interesting and personal subject. It is kind of subjective, but I will provide a few reasons.
Reasons:
His appearance ( he was black and big, exactly 350 pounds and 6ft 3, of course the cop probably assume a he was a thug)
The cigarettes: ( a black guy selling cigarettes could be selling drugs or anything else. The police probably overestimated what the guy could be doing since they really didn't know. )
The report: anyone could have reported Garners presence infront of a beauty supply store because they were suspicious or found him a threat. Police often act off or reports instead of having the patience to watch observe and investigate. They probably already had stereotyped him as a person that was dangerous.
