Apple solved the problem in China with surprise inspections done by independent organizations (e.g. the FLA); e.g. see

https://www.theguardian.com/technology/2012/feb/20/foxconn-r...

The title oddly enough is "Apple faces its 'Nike moment' over working conditions in Chinese factories" from 2012.

One challenge here is that the host government (local, provincial, or national) is often complicit and might not agree to allowing such inspections. In that case, you simply have to be ready to walk away.