There are few issues here.
1. Regarding extending of shelf life: In my factory, we have 3 quality issues regarding shelf life: microbial levels, moisture levels (our prducts are dry powders, so increase in moisture can cause spoilage), and essential functionality properties (such as taste, peroxide value, water holding capacity etc., different one for each product).
I regularly extend shelf life- I get a representative sample, test it for these 3 issues, and if the product is still inside the parameters we defined (and validated by our R&D team), I extend shelf life.
Of course, this is not relevant to perishable and fresh products, or to any product where the shelf life is clearly defined by a standard or government regulation. Thankfully, our products are not part of this.
2. Regarding sell of out of shelf life products: we have a nice case here. An improter who had a chain of stored. He'd buy close to end of shelflife products (usually high-class candies, such as tobleron or lindt), and sell them much cheaper. We always know to check the shelflife before purchasing. But about a year ago, a reporter found out that he put a new label on the product (needed anyway because the need of translation) and then put "normal" shelflife. There was a cryout. I can't find really cheap candy anymore.
3. Regarding consumption of expired products: in my family I am considered the "expiry taster". I am asked to say if a product is still good and consumable. My criteria are usually as follows:
1. If the package is damaged- throw it away. It includes, for example, rusted tins.
2. Any obvious spoillage: positive pressure in tins, mold growth, etc- need I say more?
3. If the expired date is looking too much (for example, over a year on a 2-year stable tin of tomato paste), I'd rather not test it. But that's more than a hunch than anything else- I once ate a 10 year old tuna can and it was better than fresh.
3. For shelf stable products, I otherwise take the expiry date as a recomendation. As long as the smell is okay, I taste it. As long as the taste is okay, I use the product. If the taste is not okay, than I try not to throw up but throw away.
4. For dairy products and chilled salads, I take the expiry date quite seriously, but for FIFO cause, usually. As long as the product doesn't spoil (mold on cheeses that needs no mold, curdling of the milk, such as. Yoghurt and butter never spoils), it is consumable. One exception: if the smell or taste changes, I throw it out immidiatly.
5. For ready to eat dishes, usually frozen leftovers, I try to smell. If no untypicla smell occurs, I overkill it in the microwave to kill any bacteria that tried to grow there. And then I don't let anyone else to eat it. Little toxins are good for the phagocytes :)
4. Regarding sale of almost-expired product: if the shelf life is dictated by law or regulation, don't even bother. If the shelf life is self-defined, than I think you can sale them, but make sure that it's more than obvious that the shelf life is very short. If people are bothered by end of shelf life, they won't buy; if the low price is an incentive, they'll know the tradeoff (and will consume it quickly). But never, NEVER suggest in any way that the producer is sanctioniong consumption after shelf life unless you have the proof that the product is stil lin good quality- otherwise, you're liable.
