I may not want to take a compliment because I feel too polite to, or I see the flaws so much I feel like a fraud to accept it. But by not taking it, I'm saying: "no, you're either wrong to like this or lying about it" And that's WAY more impolite than just saying 'thanks! I appreciate it!"

... and also if you just accept it when someone tells you your work is good, eventually you might believe it.