We had a customer with a very challenging floor.
What should have been a one-day sand took three days of excruciating work. But the customer was a trooper and didn't cut any corners; he followed our advice and he managed to truly save that floor. On the morning he was scheduled to apply his finish, he called us to complain that his floor was covered in a waxy residue. We asked if he had done anything to the wood overnight and he admitted that he was worried about the dust left on the floor and went to the hardware store in search of a solution.
They had sold him a half a dozen tack cloths and he had scrubbed the floor with them. I sadly informed him that his finish would not adhere to the wood unless he sanded the sticky substance off.
He was understandably very upset and sputtered, "But the guy at the hardware store told me to do it!" And I quietly asked him why he trusted the guy at the hardware store to know more about his floor and its planned finish than we did.
Without a word, the customer loaded up the big equipment, sanded his floor one more time, and applied his finish. He was a day behind schedule, but the floor turned out beautifully.
We all learned a great deal that day: we are now more vocal in our dislike of commercial tack rags, and my customer learned the importance of sticking with a reliable source.