you would do well to make a customer pay a lte payment charge unless you actually had a signed agreement!
i have done it once! and they paid it!
i did a clean for them, and a week later they complained about it. so i gave them 50% off, 2 weeks later still waiting for money.
sent invoice reminder, and a warning that the late payment charge will be added if not paid with in 14 days.
14 days later no payment, sent final notice with the late payment charge on and a warning that if not paid with in 14 days court action will be taken
2 days later the whole amount and late payment fee was paid into my bank! if they paid the first invoice they would of only paid £6! in the end they paid £17!