ACB's experience reflects my own and probably yours, or you would not have asked the question.
The questions that come to mind relate to the nature of the business; whether someone verified that the both people work for the same company and that your customer is a direct report to the person who is making the payments; the role your customer plays in that business; whether the aggregate amounts involved reflect reasonable compensation for that role; whether you have talked to the customer personally or are relying on what an intermediary told you, etc.
It's an unusual fact situation and the amounts involved would seem pretty substantial to most of us. The fact that there is one somewhat plausible explanation does not mean there are no other possible explanations... Sorry, but you need to do a great deal of digging before you know enough to make a confident call on this one.
_________________________
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.