You have the right to completely understand the costs of anything you purchase - this also goes for payday loans. In fact, by law (The Truth in Lending Act) you must be informed in writing as to:
Additionally, Congress passed a law called the Fair Debt Collection Practices Act (FDCPA) in response to irresponsible and often abusive conduct by collection agencies which seemed to be causing increased number of bankruptcies.
This law is targeted to those who regularly collect debts whether it be a collection agency or a lawyer. Debt collector's behavior is restricted by law, even if the debt is legitimate.
You can read about the FDCPA here Some of the conduct restrictions included in the FDCPA are: