some people say you will get spotting if you WFP a window you have previously cleaned with fairy which i find is utter rubbish.
I WFP windows we have cleaned with fairy and they come up perfect.
100% correct! IMO it was just a theory that's snowballed out of controll, like many things regarding WFP!

Does make me laugh though-
We have pure water that's ultra agressive. So much so it rots wood, strips polish off cars even puts holes in T-shirts

! Oh, & it's sterile!

BUT THEN- it can't shift a micro-film of water-dissolvable washing up liquid!

Yer gotta laugh ain't ya?