please and thank yous

so i grew up repeating one saying, "with good manners and a good education, you will go far in life". i don't know how many times i heard my mom tell me that (thankfully!), and how many times my heart was broken as a child when others did not afford me the same respect. . . but that draws out the real question, is there such a thing as being too polite? (not imho but) i'm beginning to think there might be, because people who consider themselves 'very polite' or 'helpful' tend to lean on me for help. and naturally, i cannot refuse despite the time and effort that goes unacknowledged. but how do i continue lending a hand, arm, ear, brain, etc when all i'm getting is a hairy cold shoulder?