Oh really? I would like to see the statutes. I'm pretty sure there is no federal regulations and I know there are no state regulations in PA. Please DO NOT conflate the taking back part and the reselling part. There is absolutely no law that prohibits returns or what would we do with recalled medication? What happens with a dispensing error? What happens if the doctor makes an error? What if you gave the brand, but they want the generic? What if you have a defective inhaler or a batch of pills that are crushed?
Now that you have the medication back is where the problem comes in. Most states prohibit the reselling of these items. You are free to refund them and take a loss, just not free to resell them.
I looked on line and searched the Code of Federal Regulations. The best thing I could find is his article from Drug Topics.
Can prescription drugs be taken back from patients?
Unless you have a citation to backup what you say, I would say this is just another case of pharmacists inventing rules and regulations that do not exist.