It seems to me that all you need to gain above average return is to identify someone who will accept below average returns.

For a long time US shares that paid high dividends were disadvantaged from a tax perspective compared to those that paid low dividends. So if you are a zero tax entity (retirement fund) you could reasonably consistently outperform by selecting those companies which pay high dividends.

I work for a company where we are first banned from trading for a period, then given shares, which we must then sell over a certain period to get a particular tax treatment. We always feel that the shares trade lower over the period we must sell. And higher when we can't sell.

These are all fairly public, and I think just the tip of the iceberg.