As a newb to the tile cleaning racket you want to pre inspect all ceramic, porcelain and stone counters, floors or walls from many angles under different lighting conditions. Look for any shine or glare on the grout. Unless it's epoxy grout, there should be none what so ever. Bring a flash light, some spotting kits, a metal toothbrush, rags and a knife or razor to do your inspections.
If there is a coating, chances are it's a water based product like Zee mentioned, good news is that a simple VCT floor wax stripper will take it off. it wont be quick and easy but it will come off. If it's an epoxy or lacquer coating you'll want to pass at this point in your young career.
The point of this is, if you start cleaning a job that you priced out for a couple hours work, and all of a sudden because your high heat, high alkaline and high pressure methods are starting to remove an existing coating, YOU are now on the hook to get it all off. Which if you're not prepared equipment or chemically, could take days to a week to get it all off.
