I do a lot of builders cleans and they are hard work but can be good earners if you are willing to wait up to several months for your money.
How much should I charge for each house type - ones already initially cleaned and ones not?
Work out how long its going to take to do the job and price it on what you want to earn.
How should I address the scratched glass issue?
What i do before i clean any property is walk round and and make a note of the condition of the windows and give this to the site foreman/Agent
That way i get no problems.
Should I hire an industrial vac to clear the frame openings out?
No forget that just wipe it out with a damp cloth.
How can I ensure that I will actually get paid? SHould I draw up a contarct? If so, suggested wording please.
Just print up what job you are doing and the date, who for and get them to sign it once the job is complete.
I have never had to do this myself.
You will get paid but not to quick in my experience.
Paul