not the best response

When you click on that blue phrase you are giving that post the best response of all in that discussion. It is best to wait until many people have responded before you rate best response - about a week, some wait longer. You don't want to rate it too soon because another, better response could come along later.

Best responses are good for the posters. I believe it ups their star rating/popularity and may even add to their earnings.

That means that the person who started the discussion hasn't decided who gave the best response. You can change that by clicking on "mark as best response" near the username you think has given the best response.

People pick their best response in many ways. Most pick either the one that fits most in what they are trying to convey in the discussions. Others pick the one who has the best point. Still others pick the one that best answers their questions. There is no time limit for doing this, but most do it when their discussion slows down.

Well, if it is your discussion, it is up to you to pick the response that you think was the best.

Beside each name you will see "pick for best response" or something like that.

click on the name you want and then at the top it will show that you picked them for best response.

u dont have to do ahything.. its just a sign for you that u can reply to the post in a nice manner hopin to get a good response

The user (i.e. the person starting the discussion) has the option of selecting a "best response" for that discussion. If you are the user, you can correct it simply by selecting that best response. If you are not the user, you can't do anything.