We were all in your shoes once, well most of us anyway.
As a CFI I’ve been offered right seat in a KingAir 90 and in a Mitsubishi.
Politely declined as it was a sketchy operation under Part 91 subpart K.
I’d make a phone call to the local FSDO and pay them a visit with a list of questions and take some names.
On this date ASI so and so told me this.
Then go from there.