There are two main reasons to avoid the use of collection agencies (except as a last resort).

First, they take 50% of the amount they collect. So once they get involved any profit and most of your costs are gone.

Second, they only care about collecting the bucks not retaining the customer. So their actions often flirt with the border between legal and illegal (forget ethical they usually are way over that line). They have even been known to attempt to overthrow the bankruptcy laws in their quest to get that last penny from people who have nothing left.

Using a collection agency should be the LAST possible option. Besides, most of them will only do consumer debt.