Manners?

Are they really a difficult thing to teach? I mean, I am the first to admit parenting is hard work, my kids are far from perfect, etc...but please and thank you were just automatic lessons as soon as they were old enough to talk. And it wasn't difficult..."what do you say?", "good job", etc. A child came by 15 minutes ago to sell Girl Scout cookies. I wouldn't have bought any, but the kid is the daughter of a friend of a friend...and my mom yelled for me to come up "Girl Scout cookies...." So, as my mother peruses the order form I say hi to the kid (not returned), ask her what's going on (mumbled "I'm selling Girl Scout cookies, obviously"), etc. So I look at the form, order 2 boxes, and hand back the form. She turns around and walks away. No thank you, nothing. She hasn't even hit the snotty tween ages yet...I wanted to grab her and ask her "what do you say?", but I didn't...but I did come down here to vent to all of you, my fabulous readers, who no doubt had your children (if you have any) saying please and thank you in the womb.