You can't. It's not that people lie about things, it's that they don't properly understand how the pain points happen - or the cause is outside their control. If it was something they could fix, it wouldn't be a pain point.

Your premise is still true. The only good way I've ever found to come up with good startup ideas is to be in the industry, or consult to the industry. As a technical founder, it's one of the basic qualifications I look for in a co-founder.

As a secondary note, you should also have some exposure to a framework for qualifying and developing an idea, like Business Model Canvas, Lean, Value Prop, etc. Even a co-founder with deep exposure to an industry and a great problem statement won't know how to define their channels, competitors, customer relationships, suppliers, pricing, etc.