The battle of over-giving and missing out

A friend sent me an email and asked to set up a call to pick my brain over his strategy. I wanted to honor my work so I offered him to get on a consult. But he came back saying, “he doesn’t want to fly blind and doesn’t have the expertise in this area, so he is looking to get my advice and is not looking to do paid coaching with me.”

I know I can do whatever I like but I am seeking some guidance for what my answer is in this situation. I don’t want to be just over-giving but part of me also feels like – am I missing out on building relationships with people by drawing this boundary. I have done some exchange work with other people but it has been driven by offering and giving from me first.

I just find it annoying that people think they can pick your brains without paying. Any advice on handling such situations please?