The tactics that you will use to collect past-due accounts will vary, depending upon several factors such as your relationship with the customer and the reason for nonpayment. Conventional wisdom holds that you start your debt collecting with a letter gently reminding the customer that the account is past due. That letter is followed up with still more letters, each one becoming a little more threatening than the previous one. After the sixth or seventh letter, you've threatened them with collection agencies, lawyers, and lawsuits. Sometimes it works, but most often it doesn't.
Most people know how the game is played.
They know that if they receive the gentle reminder, they still have a few letters to go before they have to get serious about paying the debt. If you want to start with a letter, consider paying an attorney to write it for you. However, the attorney's letterhead serves to show the debtor that you are serious. Letters are the least effective technique because they can be so easily ignored and because you have a relatively limited opportunity to exchange information with your customer. If letters are the least effective method, then personal visits are the most effective.