How much did you believe the presenter at that moment?
I hazard not very much.
"That's a great question" is auto-pilot language for presenters. That phrase is a placeholder, which was originally taught to presenters to help them engage with their audience. Now, it's the aural equivalent of eating sugar packets.
Next time a question comes your way in a presentation try, "thank you for asking that" or "I plan to address that in a few slides, may I answer your question then?"
You'll be more believable to your audience because you're engaging them as intelligent individuals.
Let's leave "great" questions to those that generate an "I don't know" response. What do you think?