if they say "no thanks not in this weather" i explain to tham (again, since i would have already explained this to them when i first started cleaning there windows)
i garentee any work i do for 48 hours regardless of the weather i work in, plus rain water will not affect the clean, dirt gets windows dirty not rain per se' (sure rain can pull dirt out the air and from other sufaces)
look at it this way if you have adirty wondow and i clean it then it rains its still relativly clean, plus im full time so i need to make this job pay!
and finally if they insist they still dont want them doing i mark them down with a strike. 3 stikes and there dumped!