Ford Motor Credit and Nissan Motor Credit were both charged with disparate treatment because of differences in auto pricing. Nara Bank in CA was charged for charging white borrowers more. CFPB has a special task force looking at indirect lending.
Take those 4 then re-read the above posts. If it is not based on risk or relationship, it might be hard to explain why there is a difference. In addition, if there are pricing breaks because of credit score, LTV, etc. they should not only be in policy, but universally applied, and exceptions (if any) recorded, analyzed and reported.
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Integrity. With it, nothing else matters. Without it, nothing else matters.