Actually, it does matter how much you paid for the account because that is not how much I would speculate the prayer is for against the defendant . . . correct? That is too say, that if you sue someone for 5k, they should be concerned with whether you paid that amount insofar as they can estopp you from unjustly enriching yourself for more than the amount paid. It's a simple matter of equity that someone who purchased an account from a third party for $5.00 should not collect $5,000.00. I am not inferring that you do this or even that it's not a sound business model rather, only that it is a matter of "concern" for those facing a judgment.
What we pay for the accounts has no bearing on the balance owed. The contract the debtor signed says they are responsible for all late fees, interest, finance charges, and sometimes collection/court costs. The account I was referring to I paid about $500 for and the judgment is for about $13,000, and adding judgment interest daily.