We guarantee OUR work. We know HOW nice your windows will look when we are finished cleaning them. We have been complimented enough on OUR work that. We are confident that YOU will BE happy with the END result. If someone has NOT HAD their windows professionally cleaned before. They might NOT realize HOW much work goes into moving ladders around the outside of their home or inside to reach the high ones (especially the unreachable. Annoying ones that YOU SEE HOW dirty they are when the SUN shines through). If YOU are NOT totally satisfied YOU Don't have to PAY the bill.