About the "bother" factor: right after I've taken time off from work to drive to a grocery store, spend a half hour or hour or more finding the things on my list, paying $50-100 or more for them, loading them in the car, driving back home, unloading the car, getting frozen things in the freezer and fresh things in the refrigerator and everything else put away, and starting to make dinner--by which time I've been either standing or driving a car for between an hour and two hours... right then, and probably for the rest of the evening, it's too much bother (and time, and gas) to go back to return $3 of bad produce, if I even happen to notice it then. Ugh. And I'm sure the stores know it's too much bother.
One thing I try to do about something that's gone bad before I bought it (say, produce or chicken or milk): I call the store right away, get the customer service desk and say, I was just in your store (a few minutes ago, or last night, or whatever) and bought X and got home and found out it had gone bad. They generally always say, bring it back and we'll give you a refund. I say, can I bring it back sometime in the next day or two? I just got home and am trying to make dinner; I can't drive all the way back there right now, and they say sure. And I ask for the name of the person I talked to and I write it on the receipt and circle the date and time. Then I put the receipt in my wallet, put X in the fridge, and take it back the next or next-next day when I am out again.
This motivates me to make the stop to return X and get my money back while I'm out running other errands, rather than making a special trip, which I know I won't get around to making. I'd like to think it also gives me some credibility when I show up to return X that I didn't just wait for a few days for it to go bad before trying to return it.
So I'd say it is worth it to me to return food that went bad in the store, if it can be combined with other errands on another day rather than requiring a special trip. Whether the store tracks it and looks at their handling processes or talks to their supplier or chalks it up to shrinkage or does nothing, I don't really care (except that if it happens more than, say 2 or 3 times in a year I'd probably steer clear of that store in the future). I assume they're watching their bottom line very closely, and how much attention they should pay to the various factors that influence that bottom line is their research project---their mission, if they choose to accept it---not mine.
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