I find myself in similar situation all the time and one yearns to correct these people:
Dear Miss Manners:
As the communications director for a government agency, I respond to written constituent inquiries. In an effort to personalize my responses, I often excerpt from the original missive. For example, "You're agency stnks!"
Should I correct spelling and grammatical errors from the original correspondence or leave them as is? I hate to fudge a quote, but if I don't correct errors, I am concerned the constituent will think the mistakes are mine, putting my agency in a bad light.
Also, it seems rude to point out someone's errors when they have taken the time to share their concerns. My agency does not yet have a policy regarding this point of professional etiquette.
But if you correct the quotation, won't the letter writer think, "Stupid bureaucrats -- can't even quote accurately"?
Besides, surely it is a comfort to note that your critics are not, shall we say, discerning.
Miss Manners would consider it polite enough if you preceded the letter writer's words with "as you so colorfully put it . . ."