Since you can't squeeze and egg to check its freshness, here's a quick test you can do at home!

Oh great, the video stopped working...basically it showed someone dunking an egg into a bowl of water. Sinking or floating told you the difference betweeen frresh and stale.

 Don't know how the store would react if you brought a bowl of water there and started dunking eggs...but this is pretty interesting!

 On the side here are some pictures of an oddly shaped egg...my son called it the nipple egg....