First of all, have you got the machine to cope with it. Most Tile and Grout cleaning is carried out at between 800 - 1,300 psi. Obviously you need a large recovery tank or APO system, as well as a large fresh water tank or feed.
There are plenty of floors domestic and commercial in tile and grout, but its a bit slow to get going as most people manage with diy mopping, however if you dont give it a go, youlle never know. Think of it as an additional service.
Dave.