In many cases, the collection process is not fast paced or particularly attentive to debtors, and they simply `slip through the cracks'. Most collection agencies are simply not up to the task, and you can avoid them by a variety of methods. For example, by making a promise to pay, and then paying a lesser amount and marking it paid in full, you can create a lot of confusion for a collection agency. This may get you put into a dispute situation in which your case is ignored until you can be contacted. You can often do this several times per year, cutting your payments to almost nothing. At the end of the year, the case may be marked as uncollectible and not worth pursuing.
Although the statute of limitations varies from jurisdiction to jurisdiction, 4 years is normally as long as you have between the last payment and filing suit. A debtor who knows the statute of limitations can often hold out with trickery until the statute expires, and then escape without legal recourse to the creditor. A clever lawyer I know talked a debtor into making a small payment to `show good faith' 5 years after the debt went unpaid. The lawyer could not have sued had the debtor refused to pay, but because the debtor made a token payment, the lawyer got another 4 years to sue.
In many cases, if you ignore all letters and have an answering machine, the collector can never get in touch with you, and eventually drops the case because it's below a suit threshold. The basic trick of never getting the message is important in getting past collection agencies, but a good collector will note this, and when seeing it several times, will immediately send the case into a law suit regardless of the amount.
It is important to keep the trail as hot as possible. Many bill collectors make the mistake of `working a case to death'. They will send tens of letters over a period of years without any payments coming in, and then forward it to a lawyer. Other collectors will do almost nothing on a case for many months, and then try to get payments. All of these things work against the collection process, and cause undue delays. These delays convince debtors that your bill is less important than other bills that are better pursued, and if they have to make a choice, the squeaky wheel will get the grease. However, remember that if the wheel squeaks too much, they may abandon the car.
A common tactic is to promise to pay, and then call on the payment date to tell them you can't make the payment because your checkbook is short on funds. You then negotiate for a much smaller payment. If the collectors aren't well coordinated, the person answering the call may not be the same person who negotiated the promise, and you may be able to get another promise for a lesser payment at a later date. If you do this regularly, you can often keep the agency in a mode where it always thinks you are going to pay and never moves further in the collection process. A good collector will listen to your story but refuse to lower the payment amount and allow the case to proceed as if you didn't call.