How are you supposed to get enough insight from any working fund manager to determine whether something is a ponzi? It’s not like they give you access to the books.

Mutual fund and ETF holdings are public information. Random fund manager? Good luck.

Pretty sure even private hedge funds have to disclose to their clients exactly what they hold, not Madoff's "just trust me bro" promise.

Madoff operated for close to twenty years before being exposed. He was regularly lauded for being the best by well informed people. What is an amateur supposed to do?

If the argument is, “Nobody is that good, you should know better”, does that mean Buffet’s scheme will start crumbling any day now?

Well yeah that's why Ponzi schemes suck. Why should it be acceptable to profit from a Ponzi scheme? It's not your money at that point, whether you realise it or not.

> What is an amateur supposed to do?

You have two options.

1. Don't be unlucky. [1]

2. Or, you can make sure your society has socialized old age pensions, and that it puts in the work necessary to keep them solvent, and its citizens taken care of once they are past their working years.

[1] The easiest way to not be unlucky is to buy into a boring, diversified index fund. Berkshire may be a fraud, but it's unlikely the entirety of the SP500 is.