Keep this in mind: Even if you think you may owe the debt to the original creditor and the collection agency approached you to collect, would you just pay someone that you are not sure you owe? No you would not. Here are some questions:
1. How do you know that the collection agency is actually collecting for the original creditor? What legal documents does the collection agency have to prove that they are legally authorized to collect for the original creditor?
2. How much is the original debt? Have payments already been made toward the account? If so, where is the accounting of the debt, including all interest and fees? Are these fees and interest amounts legally collectable?
3. Do you really owe the original creditor money? Or do you owe a third party? Where is the contract expressing that you made the deal with the original creditor and any of their affiliates?
If you remember to keep all the legal questions out of the conversation when asking for legal proof, you'll have an easier time figuring out what to ask a collection agency for when validating the debt.