Trusting groups over individuals

Which group/community/individual we are talking about matters more than whether we are talking about a community/group verses an individual. I trust Zvi over the CDC, but I trust the CDC over the crazy man yelling at my local streetcorner.

"trust" is multidimensional, and it matters a lot WHICH groups, individuals, and topics you're considering.  Also, you should notice when you have to make this choice - it's a sign that something's odd when groups and individuals are giving you significantly different advice.  

To generalize a bit, individuals can make subtler and more customized recommendations. Individuals can be loyal and caring for you as an individual.  At the expense of more easily being biased and variable in competence and motivations.  Groups and corporations are fairer (in that they don't have personal loyalties or treat you as a distinct individual), and often can put more rigor into their understanding and modeling.  At the expense of not caring about you, except in how you impact them and their goals.

Note that groups comprise individuals.  When you're considering interaction with a group, you're wondering about the intra-group mechanisms for suppressing dissent and variation in opinion.  Some groups on some topics have the ability to guide consensus to get better results than any individual, some are closer to the average or worse-than-average of the individual beliefs/preferences.  

A shorter answer: don't trust either one.  Instead consider their statements and actions as evidence to update your beliefs, weighted by how surprising it is that such statements can come out of those mechanisms.