Ask HN: Strategy for dealing with timewaste biz-dev meeting invites?

Lately I've been finding myself in conversations with people claiming they want to discuss a partnership between their company and one of my projects. As these partnerships sound good on paper, I take the meeting and we talk.

About halfway through some (not all!) of these meetings, my spidey-sense starts tingling, and I realize that either

a) This person does not have the authority to do the deal that was used to get me out here.

b) This person is really just trying to pitch me on their idea and the partnership thing isn't a two-way thing.

I like hearing about what people are working on and understand not every idea works out, so I'm not bugged too much when this happens, but I was wondering if people on HN had similar experiences and how they dealt with them. When I first started WindyCitizen.com, I was desperate to get anyone to listen to me and understand that feeling, but I'm pretty busy and my time is important. Someone getting me excited about a deal that's not really going to happen is frustrating and a waste of my time.

How do others handle these sorts of invitations? I'm half of a mind to start requiring some "proof of seriousness" before entering some of these discussions.

I'm also now of a mind to just disregard most if not all of these "let's work together" offers unless it's a clear "you pay me for X" or "I pay you for X."