Observation is probably the best method. I rarely have found form options to be effective. A good chunk of 'good' people tend to get filtered out from my observation.

Generally the approach that has worked for me having a tier system. People who meet your criteria get greater access etc over time.

> How are "good" and "bad" quality of people categorized?

Generally, "good" is anyone that helps your community prosper. "Bad" are typically people who cause unwanted conflicts, create a toxic environment etc.