Can a physician be convicted of a conspiracy to pervert the course of justice where the principal government witness at trial was a federal agent?

In United States v. Badia, 490 F.2d 296 (1st Cir. 1973), the conviction of a physician was affirmed where the principal government witness at trial was a federal agent who testified on three occasions he called on the appellant at his office and was either directly sold controlled substances from appellant's stock or sold prescriptions for controlled substances which he then had filled at various pharmacies. The court felt that the jury obviously believed the agent's testimony and its conclusions that deliveries had occurred which were not within the usual course of appellant's medical practice were warranted. The court concluded: