I mean, define “well executed”. Theranos, in particular, it’s notable that very little of their money came from _conventional_ sources (traditional VCs, sovereign wealth funds etc). It was largely, essentially, _personal_ investment by stupid rich people; often via a family office, but ultimately at the direction of the stupid rich person. IIRC one attempt by Theranos to get investment from a real VC collapsed because they _could not provide audited accounts_. Like, they didn’t even have a fake set, they were not providing them to their investors _at all_.

I don’t think that any of the named ones were particularly well-executed, and people were trying to warn that all of them were problems for a while. Madoff might be the closest, but even there it was verging on being an open secret that there was something up; again, Madoff’s investors were not actually that sophisticated.

As a "poor" person by Madoff investor standards, I am paranoid of any investment where I don't know what it is invested in. That said the other side are people who invested with the guy who bet against the CDS crap in 2008 (sorry forget his name), who I think were also in the "trust a guy with my money" camp. So I can see why people do it. But I would diversify, maybe max 10% in any one fund that is a black box, maybe max 40% in black boxes in total. Assuming you are rich - maybe 10% for most of us.