As a former executive branch employee, the required ethics training is clear: the appearance of a conflict of interest is just as severe as an actual conflict of interest and we were counselled to avoid both at all cost. If that means it is inconvenient for you or a contractor, that’s too bad because impropriety in government dealings is unacceptable.
This is codified in many areas, such as any employee - up to and including the president iirc - not being allowed to accept gives or honoraria above a fairly low financial threshold.