Why not push it all the way to the consumer? Why shouldn't you be liable if you buy a wrench, but actually the worker who made it was mistreated? That would make people think twice before buying products of unknown provenance and supporting slavery.

The customer is sometimes liable for a purchases. If a person go and buy a known stolen item, pay money to known criminal activity/terrorists, then they may end up being punished for it.

The relevant question is what knowledge the buyer had, which the Court of Appeal did consider. Dyson UK companies and personnel was aware of the crime being done by the supplier.

The general legal question is not if a customer can be held liable for purchases. They can. It is how much due diligence is expected before someone should be held liable.

In the UK, if a homeowner (customer) pays a company to clear domestic rubbish, and the company illegally fly-tips it, it's the homeowner who gets chased. The law requires them to check that the company is legit.

I considered this too, but I think it's unreasonable in the end, since there seems to be a fundamental difference/motive between an individual consumer and an entity trying to generate profit. A consumer should be able to trust that the product they're buying was manufactured in an ethical manner.