"Clean" is relative. What is considered clean in Chabad isn't necessary clean enough for others. Just ask the Esrogim sellers in CH who makes them most crazy on cleanliness.
I once heard a story from Rabbi Labkowsky that informs how I choose an esrog, forgive me if I forget or fudge any details: the choicest esrogim every year were set aside for the Rebbe to choose from. There was one big, beautiful esrog, the perfect shape the Rebbe typically loved, but on closer inspection, it was not at all "clean" and thus was not put aside. Then people came shopping for esrogim, and almost every customer was immediately drawn to this esrog, but as soon as they got close, put it aside. When it was time to take the esrogim to the Rebbe, on a whim, he grabbed the big blemished esrog and included it in the selection. sure enough, the Rebbe picked that one.