The conventional thinking about keeping customer service staff happy is to do things like trusting staff to make decisions, foster and support an inclusive environment and easy access to senior staff.
That sort of advice is directed to the management of the respective companies, but what can customers themselves do?
The simple advice is to treat customer service people as human beings. Give customer service to customer service people. That way they will be less inclined to be wary of the customer and be happy to do their best to help.