collections

That's called a 'pay-for-delete' letter. It works sometime, but not others. Just depends on how badly they want the money, I suppose.

I have one of those letters outstanding right now, but I haven't heard back from the CA as yet. I'll post when I hear something.

I would venture to guess that a pay for delete can work in some cases. I would think your odds of it working improve greatly if they have a weak case.. and you can prove they have a weak case.. ie.. no real validation.. debt is out of sol, they've violated fdcpa etc.
If they have strong documentation, and a solid case against you, I doubt they'd be willing to budge unless , as stated above, they really, really want the money.