Since I went WFP, I always think 4 weeks is too soon, it comes round too quick for me. The glass is always still clean for a start and I got the impression some would rather I waited until there was at least some dirt on their windows to actually clean off. Took on some more work and now I go mostly 6 weekly and sometimes it can be seven, no one ever seems to notice to be honest. Money wise, I never seem to notice either. I look at my wallet and it is always big and fat these days so I just mosey on down the same road.