I have several stones from Dan's. All have been dead flat from the factory. They cost a little more than other companies, but are worth it because they are truly lapped. They can be lapped flat with SIC powder and a piece of glass, but it will take a while.
Many around here Have bought from Dan's. I have heard zero complaints about them. Dan's stones are the only ones that are known to always be flat. I wish I had gone the Dan's route. But, then again, I did get a very good workout flattening my Arkansas Surgical Black, bought from another vendor.
My Dans Surgical Black Came Flat..But..To Check it..Draw Some Lines Across the Stone with a Marker or Somit & Lap it with Figure of Eights..If the Marker is Completely Removed the Stone is Flat..If Any Marker is Left Behind Keep Lapping it Until they are Gone.. Billy..