I read an interesting book about how to approach customers and friends about your startup. The main thing is: don't ask biased questions and don't ask directly

I read an interesting book about how to approach customers and friends about your startup. The main thing is: don't ask biased questions and don't ask directly about your idea. Instead of asking "do you like the idea", "will you buy my product" ask about "do you have such problem", "which tool do you use NOW to solve this issue", "have you looked for some paid solution" and so on.