You try to acquire the relevant information and data. You ask your broker (GS, here), what the information is that they have, rather than just accepting their "Good Value" label. If that information doesn't meet your requirements for "due diligence", then you don't invest in that company.
Also, it's not particularly important to be able to claim due diligence.
Also, it's not particularly important to be able to claim due diligence.