I always include a "thank you for considering...." or "thank you for your assistance," etc., when asking a question or a favor. If they can help me or they can't, I usually will dash off a quick "Thanks" or, "Thanks for trying" in reply. I like to let them know I appreciate their efforts, successful or not.
I learn something new every day, but not everyday!
I've learned to never trust spell-check or my phone's auto-fill feature.