There are two issues that haven't been covered in the above:
#1 - Verify if you are dealing with the collections department of the original creditor or a collection agency that bought the debt. The rules are different depending on which one you've got. And don't just take the company's word for it. Call your original debtor to see if the debt has been sold or not.
If you're dealing with a collections DEPARTMENT, then you really do owe the company the money and they will benefit from collecting the entire amount. If they accept a lesser amount to retire the debt, they can send a 1099 for the difference because you really did profit from the pay-off and they really did lose money in doing business with you. Dave Ramsey talks a lot about the moral responsibility to pay our old debts. In this case, I think he is right.
But a collection agency is much different. Your original debtor sold the debt to this separate company for pennies on the dollars (pennies! So if you originally owes $5000, the collection agency might have paid the company $100 for the debt). If so, the original debtor has taken the bad debt as a tax write-off. In my mind, they've gotten their money. They've been paid. Anything you pay the collection agency will NOT go to the original debtor. As a matter of fact, the original debtor will have nothing to do with you anymore. Even if you called them and said you'd be ready to pay, they'd have no way to accept your money. Your account with the original debtor is closed.
So dealing with the collection agency is doing nothing but keeping them in business. Quite simply, that IS their business - buying old, noncollectable debts and hounding you until you give them money to make them stop. You know what? THEY DON'T STOP! There have been horror stories of people who have completely paid off debts with collection agencies only to have the debt come back to haunt them 10 years (or more) down the road! When we advise you to keep your records, we are being very serious!
#2 - So when dealing with a collection agency, the first step is to make them "validate the debt". They have to send you proof that you actually owe the money to them. You know what? Many collection agencies can't even do this step. If they can't validate the debt, you're home free! They even have to take the bad debt off your credit report. Which, BTW, is one way you can tell if you're dealing with the collection department or a collection agency. With a collection department there will be one line item on your credit report for that debt. With a collection agency, there will be two - the old one with the original company (which will say "closed") and the new one with the new company which will be active. It just takes a long time for all that to show up so don't rely on your credit report.
Anyway, if the collection agency can validate the debt, then you start negotiating - IF YOU WANT TO! Remember, you no longer owe the original debt. If you pay the collection agency all you're doing is keeping them in business. Because they paid so little to acquire the noncollectable debt, if you pay them anything to close the account, then they will not send you a 1099. The money the receive from you is pure profit. Wait approximately 4 years and if they try to call you, you can laugh at them because in most states after 4 years these kinds of debts are noncollectable. Wait 7 years and they completely drop off your credit report, too.
The next thing to do with a collection agency is to write them and tell them to STOP CALLING. Tell them you will only do business with them through the mail. This forces them to put everything in writing. Every time you write them, you'll save a copy and you'll put a deadline on the letter for when they need to respond. For instance, if you offer to pay them $1000 to retire the debt then make sure you state that they have to respond by mail by August 15th otherwise your offer is null and void. If they respond, then send them a money order - again, keeping copies of EVERYTHING - and ask for a pay off verification when they receive the check.
Post again if you have any questions.