You can check the statistics on your tablet. Income for each store/machine, the sold product amounts for stores/vending machines, and the total number of customer visits for each store/machine.
It's reset at the end of every day.
You can see the daily store and machine statistics in the daily report.
If you haven't already, please consider leaving a Steam review. Even if it's a few sentences on how you feel about my game, I'd appreciate hearing your thoughts!
All the best