How to tell the difference in practice
The test is whether the mark sits on the surface or in it. Soil, film and residue sit on top and respond to cleaning. Staining that has penetrated a porous material, etching from an acidic spill, wear through a coating, scratches, and discolouration in grout or sealant are all changes to the material. A cleaning method removes what is above the surface; it does not add material back or reverse a chemical change.
The quickest check is a small test area. Cleaning one square metre thoroughly and comparing it to the rest answers the question immediately and without argument. If the test area comes up, the surface is dirty. If it looks the same, the condition is worn or stained and the conversation should turn to restoration options rather than to more frequent cleaning. Doing that test at the walkthrough is far easier than doing it six months into a disagreement.
