There is nothing that empowers you as a public speaker like speaking from a place of authenticity. But if the author of the speech is not an authority on their topic, then the piece will not have authenticity.
Authenticity sells. People like the genuine. It sells the message of your presentation or speech. It also sells the products and services that you speak for.
Building authenticity comes from being an authority. Being an authority comes from real research. You simply can't speak about something you aren't deeply aware of. And if you do find yourself having to speak about something that you don't really know about, the chance that you'll be found out is pretty high.
So, have pride in your work. And start with research. Even if you know about your topic, you can still dig deep. I am constantly updating and extending my knowledge in the field of public speaking. I watch videos, listen to podcasts, I read books and eBooks, I read journals and I speak to other people about the topic of public speaking and presentation skills.
I believe it was Ernest Hemingway who said that for every 10 words you write, you should have a 100 words of knowledge. I'm not sure the maths is solid, but you get the point. If you want to make a presentation with authenticity, you have to develop a deep knowledge of your subject. There's plenty out there. And a judicious use of the internet can easily help you.
But on that topic, these days, sadly we will live in an age of Wikipedia, where if someone wants to learn about the Russian Revolution, they can get the main points from the Internet, and try to wing it from there. I had a student once tell me "I looked on the Internet, and there wasn't much about the Russian Revolution." He then read some facts from Wikipedia. No one is going to buy that.
Start with the Internet, and then go deeper.
If you want to talk about your brand, you need to know your brand - deeply.
If you want to talk about sales, you need to know about sales - deeply.
If you want to talk about this quarter's sales, understand them deeply.
If you want to destroy your competition, you got to know your competition, deeply.
What does deeply mean? It means until you are an expert. Now, I know that's not always possible. But as far as possible, become the authority on your subject.