It was Part 135 Charter and insurance and/or the company chartering the aircraft can/will require more than one pilot. The aircraft is certified to be operated with only one pilot, but you can operate it with two. I was an approved SIC and took an actual FAA checkride in the plane to be the SIC. The PIC was former airline and we did operate the aircraft as a two pilot cockpit like the airlines. On interviews, I explained this and carried the copy of the Part 135 FAA checkride in it to prove it true.

I know people buy time in the right seat of a Cessna twin, but this was different.