Doctors should keep their patients informed about being paid to enrol them in a clinical trial. Post-marketing surveillance or phase 4 clinical trials - are a signicnificant part of medical research. It involves giving patients a new drug and the family doctor reporting any problems that might arise. The post-marketing phase will involve many more patients than those who can take part in previous trials and can be an important way of revealing uncommon side effects.
Doctors will often be paid for their trouble in enrolling patients and keeping records. Researchers in the US felt that it's not always clear to the patient that the doctor is getting a cash benefit from their participation and this is wrong. It goes against the idea of informed consent - because the patient doesn't have all the facts - and it could lead to conflict of interests.