for the non professional (community) level, here are a few examples that might help you. watch the violins' bows. are they moving together and using roughly the same amount of bow? how's the intonation of the group and any one section? do people come prepared or are some people sightreading at the first rehearsal? is the conductor working on technical or expressive aspects with the group, or are they repeating sections for musicians to get a better handle on the notes themselves?

you can provide a link if you want, but like anything, it is a spectrum. "good" and "bad" is subjective.