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 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.