This happens on a DAILY basis for a variety of reasons.
For example:
1) Manufacturers provide a variety of marketing displays and pay supermarkets for the placement in the aisles. Auditors are paid to verify proper placement.
2) Ditto on shelf space.
3) Suppliers pay for exclusivity. Auditors make sure that competitive product is removed.
4) Nearly all retailers visit their competitors on at least a weekly basis for price checks in critical departments.
I have done this sort of work on occasion. Years ago, when there was an active management in most supermarkets, it was a lot harder to do. Now, it is pretty easy to avoid detection.