T+C's, contracts, unless you're dealing with a very valuable client I wouldn't bother.
No domestic customer is going to sign up to a contract, and even if they do you'll still get the " not today" now and again and even on a normal pub or shop at say £15; is the hassle of taking them to court worth it if they decide not to have their windows cleaned at any given time
We have an awful lot of commercial work and an equal amount of domestic and not one single one is under contract; even those worth £1000+ per month; they're not needed and not worth the paper they're written on in our opinion; and that's an opinion based upon 20+ years of doing this job.