This is what I do.
Invoice with 14 days to pay. If not paid by due date or next service ring and tell them no more service until paid. Sometimes they will request an extension to pay and if I agree to it I will do the next cut but no more unless all outstanding money is paid. If they do not pay 7 days after due date the reminder goes out. After 7 more days it is follow up time. I rarely get any who go beyond that and most of my customers are extremely good at paying. If they are new and I don't like the look of things or have a hunch then it is money up front. Been burned a couple of times and it makes you wary. Too many people say they are after a regular service when they are not and are only trying to beat your price down. I don't really think of them as regs until after the first 5 cuts. Stay on top of your invoices and follow defaulters up asap is the best way of doing it in my book.