My boyfriend reads a lot but only attended one semester of college so he knows words that he hasn't heard pronounced. When he mispronounces one, I wait until we are alone and say something like, "I have only heard that word pronounced X.". That way he can can save face, and I am not over-assuming, because some words are pronounced in more than one way. To be sure, there have been times when my pronunciation wasn't the most common either.
I think the same tact should be taken with any difference of thought, because you can not always be certain you yourself have all the information. "Have you considered" is another respectful way to present a difference of opinion.