While it's not an appealing idea to me, either, they don't dumpster dive for stuff that was opened or partially eaten like racoons would. They go for stuff supermarkets throw out for being out of expiration date. Stuff's so full of preservatives that it's usually still good to eat, provided the packaging was never damaged.
I've worked in a supermarket when I was in college. Believe me, you don't want to dumpster dive in those dumpsters.
Most supermarkets give away the 'still good stuff' to homeless shelters and such already. Most broken boxes of crisps and such are given to the staff.
Not to mention to take care of the smell of decomposing fish and other shit we had to basically chemically douse the bins every week.
Also, most super markets have public bins for people to throw their cigarettes in or use as vomit containers after closing hours. Occasionally piss filled bottles not taken by the bottle machine would also end in the bins.
We emptied those bins in the same dumpsters. Finally, most people consider supermarket dumpsters an easy way to get rid off their own trash discreetly that the wife/husband shouldn't find such as used condoms or syringes.
Not to mention you share your delicious meal with insects, stray cats, rats and other vermin.
It's really not a good idea to dive in supermarket dumpsters no matter what gold you might expect to find in there.
