The results of a survey of businessmen's trust in 31 provinces, municipalities and autonomous regions in China showed that half of the locals believed that locals were trustworthy. For example, the reliability score scored by Beijingers for Beijingers is 57.9. The score for Tianjin people is 15, with one exception, that is, Hainan people themselves do not trust Hainan people.
Foreigners don't know much about Hainan businessmen and give them a very low trust score would provide a reasonable explanation for the above exception.