Living on our little farm we do not have to worry if our chickens eggs are fresh or not. Simply provide them with clean water, good seed and nice comfy clean hay to nest or sleep.
Visited the local market, purchased some eggs to do the following test just to see what they are selling.
One floated quickly.. opened it up and it was green inside - yuck!
Watch this video it will help you avoid being sick at your stomach if you're into eating eggs.
Regardless where you buy them.. test, test, test.