1. I think you’re right about “labor grinder.”

2. I think they follow the Trump method of not paying people who bill them for goods or services rendered, or claiming a “discount” and only paying part. Like him, they know the creditors usually can’t afford to take it through court.

I’m guessing they mean paycheck by bills?

So they discount (lower) their employees’ paychecks?

Labour grinder could mean his workers (labourers) are worked (grinded) to the bone.