Conflict of interest
Occurs when a person is involved in multiple interests, one of which could possibly corrupt the motivation of the other. A conflict may be encountered or discovered when someone gives advice to one person, while working for another, who also gets revenue from the same person. The client is struck once by the manager, and again by his boss. 
It was a conflict of interest, when Doctors got paid by selling drugs to patients. This lead to pharmacists dispensing chemicals, instead of Doctors who are today paid by fees.
An example of someone who may have a built in conflict would be a Doctor who worked for a drug company, or a mutual fund manager who was owned by a broker. A broker owned mutual fund can churn an investment portfolio, turning investors profits into brokerage fees. The stockbroker must service his clientele at the same time taking orders from his boss, who benefits from increased trading.
From 15c to strike together, be in conflict. Phrase conflict of interest was in use by 1743.