I recently just finished cleaning 52,000 Sq ft of tennis courts.
The number one thing to do is "set expectations".
The courts I did were covered in dense black mold, so surface cleaning was a must. But you need to 100% fine tune the pressure and dial in the proper soap for pre washing.
Pick a far corner and complete a test area large enough to see the results when dry.
Using a surface cleaner will def leave somewhat visible lines, but if your set up right it's fine in the end.
Over time the lines start to fade.
Just make sure you advise them of this before starting. Setting expectations is key in this industry.
Here is a pic of half a court washed. My camera is screwed up so disregard the black spots you see.