> If the El Salvadorian gov't is corrupt enough to run an international pay-based prison, couldn't they also accept a payment, from anyone, for releasing an international prisoner?

That's the problem with mercenaries: how much do you trust them?

There's a certain balancing act in going with the highest bidder: if no one trusts you to stay 'on side' once you're paid, why would they pay you in the first place?