How many times have you contacted sales or customer service, only to be informed you've called the wrong line? Or told to fill out some online form first? Or made to feel a fool, because you don't know if you have Version 4.2?
When conversing with a customer, be sensible and humble. To show off your knowledge blunts your effectiveness.
And when it comes to customers, don't weasel. Weaseling destroys trust.
If you need to make a point with a customer, make it clearly, concisely, candidly.
How many times have you contacted sales or customer service, only to be informed the price isn't actually available, the product doesn't really work, the warranty is never, ever applicable? "You'd have known that, if you'd seen the fine print."