I think they're both equally culpable; the customer for making pricing a race to the bottom and the service provider for choosing to play said game.

The customer could choose to consider the treatment of the workers a priority in selecting service providers, and the service provider could choose to refuse to exploit their workers just to secure deals, but neither of them have any real incentive to do so. It's not illegal to shop primarily by price. It's not illegal to hire PT workers even when FT would be viable.

I do agree, though, that the problem is a lack of regulation; unfettered capitalism really does have a evil end game.