I have much experience with those legal debt collection companies as well as those gangster-type debt collectors in the past. Tell you my experience:
In Singapore at least, because of the strict laws protecting the people, debt collectors are useful only if the debtors are still financially viable, and his business or employment is still operating. But if the debtor has really reached a stage where he is already a "gone case", then dont waste your energy to go after him, just treat it as bad debts and bite the bullet.
Before 1990, those illegal debt collectors are very useful and effective. They used very creative, inhuman and illegal means to squeeze and force the debtors to pay, without any regards to the health of the debtors. But that was the past. Now even ah long also knows the limit of the actions and consequences, and consequently they are no more 100% efficient in the collections.
The other legal means are thru lawyers, etc... but usually if the debtors are really broke, these legal means are not effective at all.
Check your debtors and do some PI works yourself to save some costs and if he is still doing normal business or employment, then approach the collection agencies if you do not have the time or guts to follow up. Normally they want ard 30% -80% (including expenses, etc) depending on the SIZE of the debts.
Usually we would write off the debts if we know that the debtors are REALLY in very bad situation thru communication with him or his family members. But in the event when the debtor is very rude and unreasonable, I would have to engage these rascals to force him to pay, even to the extend of paying up to 100% of the debts to these rascals just to see justice done. Usually they will send 2 or 3 ugly looking but friendly brothers to hang around him the whole day .... that's not illegal at all if they can show the police that they are collecting debts and they have not broken any laws :dunno: 100% effective if he still have monies to pay you.
Good luck!