I do not sell my eggs but I share with some friends. I use cold water in a bucket and one of those curly round metal scrubber ( not brillo pads) I do not know why but I was concerned about using warm of hot water.
As most of you have said if my ducks lay in the grass or dry straw great if not it takes a little more. All of the mud/poop comes off but sometime I noticing a bit of a grey color that sometimes remains.
I typically refrigerate as I thought that made them last longer but it sounds like that does not matter.