He cites an article in the Journal of Services Marketing which showed, unsurprisingly, that the level of EI in customer-facing staff correlated with customer satisfaction. Interestingly, this effect was strongest in potentially difficult "moments of truth", such as when returning an item. Goleman comments:
Goleman thinks that the main driver of this link is emotional contagion - the tendency for emotions to be catching. In other words, happy staff make for happy customers. Sound familiar? This ties in well with the service profit chain and value profit chain.
One of the subtleties of understanding how customers form perceptions, which Nigel picks up on in his book, is that negative events tend to have much greater prominence than equivalent positive events. This is underpinned by our brain's emotional network, and accounts for the big difference between staff who are emotionally intelligent and others when things go wrong.