What is the ruling on the money a doctor earns if he is unable to cure a patient, but prescribes medication for him, or if the patient recovers naturally?

If a skilled physician (doctor) exerts their best effort in diagnosing an ailment and prescribing medication, then there is no blame upon them for the fee they receive, nor are they liable if they do not ascertain the exact truth. However, if they are not skilled, and their diagnosis results from their lack of qualification, then it is not permissible for them to lie to the patient, nor is the fee lawful for them, and they are held liable if they cause the patient's demise.