Increase loyalty by means of online communities. Applicability.

In continuation of the previous topic, but - separately:

A couple of common words about the applicability of communities for solving problems of increasing brand loyalty (or their group).

Communities will work where:
1. There is a job in the retail market (B2C)
2. There is a serious competition of sellers.
3. The offered products are very expensive (i.e. there is something for the seller to fight for).
4. The proposed products are difficult to understand by an ordinary person (otherwise
the site is not needed - there is nothing to talk about ...).
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From here spheres of application of such approach:
1. Personal money (discussed).
2. Auto (strange, but there is still no imputed website for people,
I studied this question recently).
3. AudioVideo equipment.

Something else on the applicability comes to mind? :)