Good question, as this is a complex sentence to diagram. We have both a "people who" and an "unless." Rather than ask which is more important, we should try to include everything in our diagram.
Advice from someone whose advantage would be served = AS Reason to think that interests coincide: RIC Regard advice with skepticism: RWS
Think about what we can conclude in this scenario: The advice giver's advantage would be served, and there is no reason to think interests coincide. We could conclude that the advice should be regarded with skepticism. This helps me to create a diagram.
AS and not RIC ---> RWS
contrapositive: not RWS ---> not AS or RIC
You can often use an "and" statement to diagram complex sentences like this one.
