No matter how many people have seen this, it is worth posting for the info of others. With the info already in the graphic, I was tempted to let the picture be self-explanatory. But upon reading the details which come with it, warm instead of cold water should be used for this test.
"A great piece of information by Klew Nu Farms
Fill a container up with warm water. I use warm water. The reason for this is. Eggs are porous. If you put an egg in cold water, it will contract and draw any bacteria that is on the outside of the shell in through the pores. This is not good. So, if you use warm water, the egg will expand, and you will notice that little air bubbles form on the shell.
Put your eggs into the warm water, and look at them. A very fresh egg will sink to the bottom and lay on it's side. Week old eggs will rest on the bottom but the fat end of the egg will rise up slightly. Three week old eggs will be balanced on pointy end with the fat end sticking up. Old eggs will be floating, bobbing along the surface of the water. These floaters should be tossed as they aren't any good to eat."
But from a practical point, we can only test eggs after purchase. Whether those eggs could be returned would depend on the retailer.
Recently, I have problems with fresh milk bought from supermarkets. That the milk was 'off' even before expiry date put me in a no-win situation. How am I supposed to prove that it was bad when I opened it? There was a time lag between purchase and putting it in the fridge. It could have been in the car when parked, even for a short while. When I thought about my loss, I actually sympathised with the supermarket! I saw cartons reduced to Rm6, and even Rm3 (from Rm12 for a 2-litre carton). To them, unsuitable conditions during transportation from source of supply, or even at production stage would put them at risk.