Hi Bernd
Here is my view on this. The tennis court carpet should in my opinion not be cleaned this way. It is one thing to like the way an encap "popps" the carpet. tennis courts are usually large expanses of carpet that are run over with a large brush machine that does not really pick up the soiling that falls into the carpet.
Next you need to vacuum the life out of the carpet to remove all the dust and muck that is in the carpet. Then where has the soil gone? It's still there and even if it has been encapsulated then it needs removing. Are you going back to vacuum it. The in house cleaners will certainly not be turning up to clean that tennis court with the correct vacuums so you will leave all the soil stil in there.
Next as a tennis player what is happening to the ball bounce - nothing. The dirt is in the carpet and you were presumeably called in to clean their carpet, not make it look clean. So when the ball bounces it bounces on the dirt not on the carpet that should be free of dirt. As the carpet gets dirtier the ball slides off the surface and makes the ball go faster, thus indoor courts gets faster and faster when they get dirtier.
The only way to clean then is hot water extraction using a truckmount for that area - simples.
Walk from that, you will not be giving the client what they want - in addition you need to discuss with them what the result will be - if you have a truckmount then do a clean on the baselines so they can see the difference on the bounce. You will also need to bonnet it off to stop the wick back.
Hope I dont sound miserable in a foreign language!!!