Just finished reading this paper: Surfing a web of trust: Reputation and Reciprocity on CouchSurfing.com.
Below are my notes.
Trust is still a local phenomenon:
whether a person will vouch for another is strongly localized on the network – depending primarily on the closeness of the relationship, followed by indirect yet still local ties
declared trustworthy, on CouchSurfing can best be predicted based on the direct interaction between the two individuals: their friendship degree, followed by the overall experience from surfing or hosting with the other person, and also how the two friends met.
Declared trustworthiness (vouches) seems less reliable than computed trustworthiness based on contextual information such as the friendship degree, type of friendship and how the two friends met:
there are indications that vouches may be given too freely. […] For example, many of the vouches were exchanged between individuals who had met through CS meetings […] these vouches artificially inflate the trustworthiness of those who have the benefit of living in cities with many CS meetings
Another reason behind the high rate of vouching may be its public nature. It can be awkward for friends to not give or reciprocate a vouch, even if privately they have reservations about the trustworthiness of the other person.