I recently helped launch a podcast that rose to the top three in the technology category. Thousands of people are listening every week. Sounds exciting, but then I realized how many people were listening to every word I said: I needed to be sure I knew my stuff.
When you don't know the facts, it's not technically lying. We see ignorance as a lesser sin and it gives us an "out" if needed. When you're dealing with a hostile customer, it may seem like a good idea to appease them in the moment with unconfirmed promises; but those always come back to bite you.
Before you open your mouth and make a claim, check your facts first. It is far better to say "I don't know, let me find out," then to make up a story and find out you were wrong. All it takes is one temporarily satiated customer to return even angrier than before after finding you gave them an empty promise, and you'll be sure to always have your facts straight.