The only problem there was the grout
I think the point is there are levels of cleaning or restoration.
To address the grout properly you may dull or surface etch the marble.
To remedy the etching you would need to polish it out.
So a front end conversation would help set expectations.
I'm doing a travertine floor next week and she didn't want it polished.
I explained that the deep cleaning process along with some food spills will leave the floor looking patchy and uneven.
So we're going to run an 800 grit polish to leave a nice even, matte / satin finish.
The point is, you offer carefully explained choices or levels and let the customer choose.
BTW 90% of T&G jobs are really straightforward. Get some TMF Grout Master, a turbo tool spinner and some microfiber flat mops.