Since 13(c) is to be construed as disqualifying any agent, broker, surety or other company from having a bond placed through or with it, if the plan or any party in interest in the plan has a significant financial interest or control in such agent, broker, surety or other company, a question of fact will necessarily arise in many cases as to whether the financial interest or control held is sufficiently significant to disqualify the agent, broker or surety. Although no rule of guidance can be established to govern each and every case in which this question arises, in general, the essential test is whether the existing financial interest or control held is incompatible with an unbiased exercise of judgment in regard to procuring the bond or bonding the plan's personnel. In regard to the foregoing, it is also to be pointed out that lack of knowledge or consent on the part of persons responsible for procuring bonds with respect to the existence of a significant financial interest or control rendering the bonding arrangement unlawful will not be deemed a mitigating factor where such persons have failed to make a reasonable examination into the pertinent circumstances affecting the procuring of the bond.