Collection Agencies for Ex-tenants' Unpaid Rent

[Chas Chip]

There are a couple of collection agencies specializing in collecting unpaid rent.  They will go after the deadbeat renter who vacated owing money and attempt to collect.  Both agencies will report the collection to all three credit bureaus.  Question:  Does anyone use these or similar collection agencies to get back rent / damages from renters who have moved out owing money?  

One advert is:  "Landlord Collection Agency, Rent Recovery Service, Contingency & Flat Fees"

another is:  "Do you have (ex) tenants that owe you money? The only collection agency for tenants."

Any comments?