Ask them if there are any windows needs special care,fragile or cracked.
I did a first clean couple weeks ago with WFP.As i was doing a bedroom window above the extension,i could only see the top half of the window,i heard the crack noise.I stepped back and saw the crack.
I ran to the door and asked her if there was a cracked window,and luckily she said yes,otherwise i was thinking about getting it replaced for them.Well,i made the crack even worse but she was supposed to tell me about it before i start cleaning,or i was supposed to ask
I feel guilty
Another thing to ask customer,is it ok if you clean their windows 8 in the morning and on saturdays even sundays.
You might need to work those days and hours when really desperate of cash.