In my experience "brain pickers" are generally looking for validation from someone they respect or that they consider to be experts. They aren't really interested in what YOU have to say unless it's what they were already thinking.

So I generally ask the large majority of questions such as "what can I help you with?" and then I follow that up with questions like "what have you found out so far... what conclusions have you come to?"

I think you'll find that they do most of the talking.

If it turns out that they truly want your assistance then move the conversation to a more formally structured one by setting up a coaching call. Any serious business person that values what you have to offer will certainly be willing to compensate you for your time.

In fact - that first conversation can be a good screening process to help you decide if you even want to take them on as a client. Anyone that is "insulted" or put off by the fact that you get paid for sharing your wisdom and expertise - things that can help them reach their goals - - is obviously someone that won't value what you have to share.

Best of luck!