When you set up an ad via your adsense account you will be asked how much you are prepared to pay each time someone clicks through to your site, usually from about 2pence per click to as much as you are prepared to go, the higher you are prepared to pay the more often your ads shows on googles affiliates publisher's sites.
If we both had ads with them using the same keywords, and i offered google a max per click of say 50p and you only went up to 10p. i would take priority over you till my account balance reached zero....... Bear in mind people click at ads randomly anyway, so you would mostly be paying for no real leads........
Personally i dont think its right for window cleaner's, as it can prove quite costy though you can claim as expenses, i prefer to stick to local free-ads and leaflets..... :
