i am really wondering how C could be an answer. It does not have any clear sense to me and miss the logic.

I think that answer should be B in case it have to weaken the argument

Though the quality of this question is suspect, here are my thoughts on it.

Two statements of interest:
The investigator found that the candidate had two speeding tickets.
The client decided that the candidate was unfit to serve on the board because he was exceedingly reckless.

From two speeding tickets, he gathered "exceedingly reckless". We need to weaken this.

A) The investigator found that the candidate had never been charged with any crimes or misdemeanors.
Irrelevant. We are talking about the client being reckless because of over speeding.

B) In the candidate's county, speeding tickets are issued on a daily basis.
Sure, it is possible that a few speeding tickets are given out every day. But considering the huge population a county can have, it is possible that most people never get a ticket. So two speeding tickets could be reckless.

C) Residents of the candidate's county receive an average of one speeding ticket over their lifetimes.
So residents on average do receive 1 ticket. This means it may be normal that rules are strict and people often end up getting a ticket. It does put into question "exceedingly reckless".

D) The investigator also located a newspaper article quoting the subject's former employee praising his boss.
Irrelevant. We are talking about the client being reckless because of over speeding.

E) The investigator found that at the candidate was found "not guilty" in a lawsuit charging him with domestic violence.
Irrelevant. We are talking about the client being reckless because of over speeding.

Answer (C)
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PlatinumGMAT Official Explanation:

In this question, the evidence – while relevant – is not enough to back up the argument. Two speeding tickets over a lifetime do not overwhelmingly prove recklessness and warrant removal from the Board.

A. This speaks to the candidate's character, but it does not directly weaken the argument that he is reckless.

B. This is an appealing answer, because it suggests that speeding tickets are a common occurrence and thus bad evidence for unusual recklessness on the candidate's part. However, if one ticket is issued per day and it is a populous county, the candidate’s two tickets could still be far above norms. Because there is not enough information in this question, it does not weaken the argument most.

C. This shows clearly that speeding tickets are weak evidence for recklessness. If most residents receive one speeding ticket on average, and the candidate only had one more than this, he appears to be no more reckless than the average person.

D. This suggests that the candidate has positive qualities, but it is not clear which qualities the employee is praising. This does not necessarily undermine the argument that he is reckless.

E. Although the fact that the candidate was found not guilty may be positive, the fact that he was involved in such a lawsuit at all could speak poorly of him. There is not enough information in this choice to suggest one or the other.
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Doesn't option C means that the candidate was >50% more reckless than the average population (PS: average of 1 ST is for lifetime and the candidate has not completed his lifetime)
>50% sounds exceedingly reckless?
Pl suggest