I wouldn't do commercial for nowt. Maybe do a deal if they are struggling and you want to keep them. Leave for a while or do parts of the jobs for partial payments.
Domestic, I'd try and keep on top of some houses for little or no payment. If they want their windows cleaned but can't pay at the moment type of customer. Ones that'll have you back when things pick up and ones that'll stick by you if you have some bad luck.