I sharpened 3 blades for a guy ( I probably have sharpened 1000's over the years ) last week, that he carried in. He took them home, about 2 days later he brought the Big Zero Turn mower in with those blades on it and said my "sharpened" blades don't cut grass worth a f***......I knelt down and looked under the deck, he had put the blades on upside down. I should have asked him how Crow tasted but, as a business....I just told what he did, and smiled!