Avoid Insulting the Customer
Obvious, right? Well, people do it without even realizing by using comments like "did you understand that?" and "are you following what I'm saying?". This automatically shrinks the customers' intelligence and ability to catch on. It is down to your own ability to make the customer understand and therefore if you feel the customer is failing to do so, use comments such as "did I explain that clearly" and so on.
Enjoy these threads from 5 years ago this week!