Promissory notes - Risk?

[Corey M.]

I've noticed that some turnkey marketers, like Norada, are selling promissory notes with really high returns (12-16.7%). These interest rates seem too good to be true. Who would pay this much to borrow when interest rates are so low? And with no collateral, how can an investor feel comfortable the money will be returned (with interest, no less). 

I did P2P lending using Lending Club. If you chose their worst rated investments, you were expected to get 8-9% returns. In actuality, I put in about 15k and averaged 2.5% returns. 

So how does one get 12-16.7% with little risk? And if this is possible, why buy houses, which come with unpredictable tenants, capex costs, etc.?