Even then you have to be careful.

It would be trivially easy to build an algo that beats the market 90% of years but 10% has huge losses. Just construct a slightly levered portfolio, with some protection against minor losses, but totally exposed to big losses.

If you sold that, it would appear like its working for awhile and you'd probably have lots of trusted customers by the time it fails.

(I'm a bit cynical, I worked in finance briefly, and I realized the fund we were selling to investors was essentially this)