The thing is, with thought, I agree with you 100%. Posting earnings will encourage folks who want to earn those figures to come into the business. I do not really like it either as I think this is just like any other business and supply and demand rules the roost.
Posting prices will also, obviously, encourage some others to come into the job. However your right, there is a big difference, because that person will have a very good idea of what he needs to charge "if" they want to make a good on going business.
The whole "polish" worker thing is a bit of a curve ball as there are plenty of british workers out there to be used for the same purpose.
There is already some on this forum that seem to be openly bragging about the fact they quote without viewing via a leaflet and then sending an employee round to clean them. Well common sense tells us that the quotes can not be big if they are getting massive responses, and the wages can't be massive either or it just would not be worth employing them.
Thankfully, it seems customers do not really like this approach to business, and thankfully the staff employed tend to abuse it too and try to get their own hourly rate up by doing shody work (either that or they just don't give two hoots). Today I had two customers say they are going to change to me within the week due to a couple of employees of this type of operation doing shody work and another one tell me they held off going to them due to the fact that they like to know who the window cleaner is before deciding.
But if enough window cleaning businesses do get jobs on price and make money just from the amount of window cleaners they have out there, then eventually it will start to kick the sole trader in the teeth.