The Federal Trade Commission maintains a list of individuals and debt collectors whose conduct has been so bad that they are permanently prohibited from engaging in debt collection activity. One must imagine that the persons and companies on the list really went off the proverbial rails. The FTC also maintains a list of its enforcement actions in federal courts across the United States. Note not every enforcement action resulted in a permanent ban.
I frequently get phone calls from consumers who are contacted out of the blue by a person claiming the consumer owes money on a debt, usually related to an old payday loan or personal loan. The caller threatens to have the consumer served and/or arrested if payment is not made within a very, very short window of time. There may be threats of garnishment of wages or seizure of property or other collection activity most of which the caller is either not authorized to take or does not intend to take. Threatening to take action which one cannot or does not intend to take is a debt collection violation. The scenario presented in this paragraph is just a more common one but by no means the only example of rogue debt collection.
If you are contacted by a potential debt collector you should demand the collector identify itself by business name, mailing address, and phone number. If you get a business name be sure to check the FTC blacklist to see if they are listed. If so, contact the FTC and an experienced debt collection defense attorney immediately. Do not commit to pay nor make any payment to the blacklisted debt collector!