Ask HN: What is one trading/investing product you want but no one is building?

I would want to fund someone's purchase and be reasonably sure that I would get paid. Credit cards charge 10%+ I would do it for 7%+ but I would need a 95%+ repayment so it would have to be in a pool of some kind.

I want a product that would tell me when to buy a stock and when to sell a stock, and would be more than 51% accurate.