Hah! I have more to report on this, and I think that its important that I do.
So I revisited all 4 of the callbacks that I had this month. One was for tile so it doesn't apply here.
Two of them were actual wickback to a very small degree, and I was not ashamed of the jobs when I saw them. The customers were pretty picky, and the wickback was minute considering the large spills.
On the fourth one, the call was about a permanent stain that I could not remove either originally, or on the callback. This stain was so light that you could only see it in full sunlight when looking from one direction only.
In conclusion, the Challenger OP method is not at fault here. I had a run of bad luck and picky customers. And since I do encourage customers to pick up the phone if they have any concerns, they did call me.
