in that case i would say that your friend has been extremely fortunate. In my experience to gain the go ahead on commercial work has taken anything from 3 months to ten months before i have been able to start cleaning so if he has managed to canvass the work, quote it , win it and expand from sole trader to ltd with 8 staff in just 3 months we could all learn from him.
thats why well priced domestic is good business, canvass, quote, win it, start it, all in the same week! in my opinion.
get paid (most of the time ) before next clean, not 30 60 or 90 days!!! or having 4/5 invoices outstanding where the company owes you an arm and a leg!