I've had to delete quite a few meaningless posts, please people, debate the issue and leave the jokes for the relevant section of the forum, a reply with nothing more than a smiley face or a jokey wisecrack only invites more of the same, and this ends out ruining a perfectly good thread.
However...
£30k plus is most certainly possible, even working trad only this is achievable....but you are not going to do this overnight, as has already been said, it takes many months just to build a basic round, then several years to hone that round into a top paying little business.
If working trad then you also need to really hone your skills, WFP certainly gives you the ability to work faster, but to go into it cold you really do need a good business head on your shoulders to understand about pricing your work and costing your business.
I would also agree with many who say that few window cleaners turnover much more than 17/18k per year, those - single traders by the way - who turn over 30k plus are way, way fewer, above 50k for a sole trader and you are getting into pretty rarefied territory.
Even were you to buy an existing, very well paying round it would still take you many months to develop the necessary skills and speed to achieve the potential returns that the round could give you.
But of course it is possible; as I understand it, there is also very good money to be made cleaning ovens....there are businesses now that do this for people, and a up to £60 a pop for a double oven no doubt there is equally vast potential in that kind of business.
A mate of mine has a one and a half ton flatbed truck and pulls in over 80k a year doing light haulage as a one man business...there is money to be made in all walks of life if you have the nous for it.
Ian