Ok get two buckets of water add Fairy liquid 2 one and gg3/4 to the other and clean two separate windows traditionally.
Next place your hands (one into each bucket) take them out - shake them off and then let them dry naturally. You will find that the hand you place in the bucket containing fairy dries sticky. This is because fairy leaves a sticky residue, GG3/4 does not!!!
Ok next bit - leave the windows to the elements. After a week have a good close look, the window with the fairy on will be dirtier I guarantee it!!!! leave it a month and the difference is really noticeable.
Why because fairy leaves a sticky residue that dirt/dust sticks to. Its a fact!!!!
When I learnt to clean windows I learnt with fairy liquid. Why because as my old boss said the windows get dirty quickly and the customer wants you back. And its true just try the above experiment.
I would rather sell a service that keeps your windows cleaner for longer, use a professional product that works out cheaper in the long run, is easier to remove from the glass and sills as there are no suds.
You can make more money from less work if your product has the edge over the competition , but hey when wfp came along most people thought I was mad then too mostly other window cleaners though!!!!