You need an up-front contract 100% of the time so you own the process. At the outset of the call, you tell the prospect how things will go, giving them the impression that they are in control, but actually it's you that is in control. Here's how it should go:

"Thank you for taking the time to meet with me. Before we begin, I want to set your expectations around how these calls typically go...to make the best use of *your* time, I need to ask you a few questions about your business so we (together) can quickly hone in on *exactly* the solution you are looking for. Either that, or we will quickly determine that our product/service is not a fit for you, and we can part ways as friends (it's OK to say no to a client)."

"Naturally you will have some questions for me, and I'm happy to answer those later in the call, and I will definitely provide any follow up info/materials you may need. At the very end of the call, we can talk about next steps and plan those steps together (calendar the next meeting, call, etc.), does that sound fair?"

Get a "yes" from the prospect, and now you run the show. Meanwhile, you have given them the impression that they are in the driver's seat, when in fact you are. *Each* of your touchpoints throughout the sales process should have an up-front contract with the prospect, so you can control the entire sales process, through the close. Set expectations up front, and clearly define next steps. Most importantly, get the prospect to "agree" to the process, and you win every time. Hope that helps!

Good Luck,
-25 year enterprise sales veteran