Remember that we are not talking about a strict liability offence here.
I won't refer to specific examples, but there have been cases in the past where the official agent was actually acting on instructions from the candidate. I think everyone would expect that, in that kind of situation, the candidate should be liable. But that is not what the act currently states.
Of course, if a candidate was acting in good faith and was misled by his agent, I don't think he would be held liable. I cannot image that a court of law would declare him to be liable.
However, in cases where the candidate himself was partly responsible for the issue that arose, I think it is appropriate to make the candidate liable.