Normally I would have, but the prescription was for Viagra, and my HMO limits me to four pills a month. If I get an extra pill, you can bet I will hang on to it. We often discovered pharmacies had added a couple extra. It was such a pain in the neck to fill out the forms to return the pills that we kept them. No pharmacist I know would deliberately short-count a patient.
Mistakes happen, but usually it's due to a machine miscount.
You would be surprised how many people drop their medicine down the drain, in their car or behind the sofa, and then blame the shortage on the pharmacy. When I had a root canal recently, my dentist prescribed pain medication. The pharmacist accidentally gave me 100 pills instead of 20. I returned them. My pharmacist accidentally gave me 100 pills instead of 12.