recently my dad, bought a carton of 18 eggs, all contained double yolks. This worried me, as I believed that it was rare occurrence.

I'm still going to tell him to ask this farmer he is using hormones, has using hormones is also a method to get double yolks

I had three double-yolks in a dozen a few weeks back.

I'm looking for them now!

I have never seen one.

I've found a few over the years. Ther's nothing wrong with them, they taste the same as a one-yolk egg.