Valroyb, sounds like your quite new to window cleaning, just do a good job be regular and everything will be OK, yeah your bound to have your ups and downs but i can assure you you'll have more ups than downs.
personally I'd stick with your domestic until you have the confidence to go for commercial work, it can be very rewarding but a kick in the teeth if you lose it, so you need the backup of your regular customers, there the ones that are always there.
When you think your ready for commercial start at the shallow end meaning shop fronts, etc there easy, quick and give you the feeling for bigger work, it wont feel such a big step up either.
Just stick to it mate there's plenty of work out there for all of us, just give a good service and you'll have nothing to worry about, keep asking questions you've come top the right place, i now the transition from trad to wfp would have been a lot harder had i not had the help from this forum.
Regards
John