Collection agencie's nightmare
Fortunately, I've never had to seek the assistance of a collection agency, however I've been contacted only once by one. It was in regard to the method employed by the receiver of a bankrupt carrier that I owed money to. It was never past due until the collection agency became involved. They were contracted by the receiver to collect any monies due.
The first contact was with a young male that was aggressively belligerent in his demand for immediate payment from the onset of our conversation. When he was finished, I stated to him that I could not even discuss the matter with him under the constraints of PIPEDA, and that my reality, was that he was merely a voice on the phone, and didn't provide any credentials whatsoever to indicate that he was authorized to act in this or any other matter. This did not sit well with him, but I was unmoved by his demands. Eventually I sent payment directly to the receiver after receiving the POD and invoice, ignoring the collection agency altogether.
From this experience, I would be reluctant to use one as I think most people are capable of downloading and filling out the small claims court Plaintiff's Claim forms. Prior to spending the time and money to file them with the court and having them served, they can be faxed or emailed to the defendant(s), with the warning that they will be filed and served if ignored. This display of intent has almost always resulted in payment. This takes place no more than 30 days past due date.