Piecing everything together, I surmised that the liquor store was swapping UPC codes on the bottles, not giving receipts to the customers and cashing them in for themselves. I called the police to report this but they said that this was small potatoes and not worth their time pursuing.
Just today, my friend Kathy went into a different liquor store to purchase a bottle of wine and like me, she chose a bottle which offered a rebate. She too wasn't offered a receipt and had to ask for it. The cashier yelled something in another language to a co-worker and he replied in that language, then the cashier printed out the receipt and gave it to Kathy. When Kathy got home, she read the instructions for the rebate and it said that the receipt had to be original and not a duplicate. Kathy looked at her receipt and at the top it said "Duplicate Copy." She is gong to try to send it in anyway. Most likely she is out of luck and the liquor store is going to use the receipt to get the rebate.
I wonder how many liquor stores have been ripping off customers of their rebates and if anyone will ever do anything about it.