a trick I learned when collecting for parties while in school, cause people dont want to pay, especially poor college kids. Take something that belongs to them. May be a little harder since you dont go in the house but when I needed to collect $25/person for a party, I would "borrow" TV or nintendo remotes, backpacks, shirts, whatever I could get. Then I would simply place a call and let them they dont have to pay if they dont want to, but if they do, theyll get their items back. Went from about 60% collection rate to 100%.
Long story short: Take their stuff