Many of us heard this advice during our formative years. In my case, my Iowan-mother incessantly repeated the refrain. She hope repetition would instill the principle. In her defense, she was fighting the "black sheep rebel" personality that was difficult to train because it is a disorder foreign to either side of our family.
My mother's principle, however is supported, in an interesting article by Douglas Hanks III in the Miami Hearld entitled, "Writers live it up; publicists get the tab." Hanks focuses on the free red-carpet treatment travel writers receive in exchange for glowing articles that stimulate tourist spend.