How do you handle any customer debt?

Michael McCormick emailed me a while ago, saying that he had taken on a Nisa Local store at Esh Winning in Durham with delivered news, and had a troublesome customer who would not pay her bills, owing some £80. He had another with shop save partworks who had stopped collecting, leaving Michael with £300-worth of stock. What recourse did he have?
Pam Hoffman, an ex-newsagent who specialises in debt recovery, runs a Small Claims advisory service. She does not charge retailers but gets her money via the debtor and the courts. She says: "It is to your advantage to have stated on your invoices/statements that, under section 69 of the County Court Act 1984, you reserve the right to charge interest at the rate of 8% per annum plus an admin cost on all late or unpaid accounts."
Where part-works are concerned, Pam suggests that orders are taken on order forms that state a refundable deposit is requested to cover the cost of one issue and that cancellations are only taken in writing. She would not recommend continuing saving part-works if there is one that has not been collected from the previous month.
Any further tips from your good selves?