Talkative? Or...Garrulous?

I recently listened to a woman making use of her good vocabulary during a prepared speech she was giving to her peers. I did not feel she was being at all showy. Nevertheless, it did not surprise me when I later over-heard people saying they thought the speaker used too many "...big words..."

Some of you may be familiar with this advice often given to public speakers: "Speak to express, not to impress". This can be a useful guideline. At the same time, I have seen this advice work against people who have a strong and natural command of words; they begin second-guessing themselves. Instead of using "garrulous" they stumble to find "talkative". Perhaps they're worrying about others thinking they're using "big words" although both have the same number of syllables. It is also possible that speakers who dumb down their good vocabularies are not giving their listeners enough credit. What is your view on this? What do you usually do if someone you're not close with uses a word you don't know?

I admire speakers (and authors) who use simple words well. I also love when someone challenges me to be smarter. Mostly, I want people to use what they have naturally at their disposal; I'll take responsibility for my learning from there.