If an overdue debt despite the best efforts of the creditor could not be reclaimed, then it is time to call a debt recovery or collection agent who is a specialist to do the job. The agents usually do not take ownership of the bad debt except in cases of flow forwarding where they are willing to pay a discounted amount upfront like in commercial debt recoveries. Otherwise they act on behalf of the creditor in recovering the amount but recovery is not always assured.
Bad debts occur due to a variety of causes: the debtor may just be reluctant to pay; he or she may be facing temporary financial difficulties which may sometimes be due to somebody else not paying them etc. Approaching a collection agency at the first instance of an overdue payment may not be always be the right approach, as most people view them with fear. The debtor may take a tough stance and the creditor may lose a valuable customer. In case of genuine difficulty in payment it is better to wait for a while, try to negotiate a payment plan, use diplomacy before contacting a debt recovery agency. The latter should be resorted to only as the last option.
Cases where it is apparent that the debtor has capacity to pay but is unwilling to do it and the obligation is established and the payment is behind schedule are the ones where it might help to approach a recovery agency. In cases where the debtor has his/her own justification and the amount claimed is disputable, approaching a debt recovery agency or court may lead to a prolonged battle. It is better to open up communication channels with the debtor and try to sort out the issue yourself amicably. Court battles usually leave both the parties concerned losers. It is also possible that the debtor is trying to combine the present debt with an old debt that you owe him. This also calls for direct negotiations without involving third parties like a collection agency or a court.
Court cases may not always result in recovery of the debt if the debtor is bankrupt or insolvent. You may win the case and yet not be able to recover the amount. Also it is better to go to court, if inevitable, directly rather than through a collection agency so that you can be in charge of the case yourself.