Owner, portrait photographer
A reliable model is a beautiful thing. Literally.
Every portrait photographer has had at least one model flake on them. If they haven't, then they're either lying or they've only photographed a model or two.
Simply, the way you get a model to show up to your planned shoot - is to promise something in return. If you don't want to pay the model, then you have to offer something else of value. And offering "prints" or "exposure" is not going to cut it. Contrary to the "dumb model" stereotype, I've never worked with a dumb model. They've all got brains to think with. Professional models are professionals. That means they do business, and that means models think.
The world of business is all about revenues and expenses. If the model isn't going to directly make money from you, offering something that could make them money indirectly is key. The mind of the professional model thinks about how to make more money just like the mind of any entrepreneur.
I once took a gig for free simply because of who I knew would see my photographs. In this case, it was technically working for "exposure," but not in the typical sense. In my little entrepreneur mind, it was a gamble. A risk. But it was worthwhile because my photos were seen by a fashion diva, and I got time to speak with one of the editors of a magazine I wanted to be in - and get advice about what they looked for in photography.
Had the model approached me asking to shoot for trade, I would have said no. But she said, "I would like for you to photograph me. I cannot pay you, but I can promise that your images will be seen by ___________." I went to her Model Mayhem page and saw that she had the professional experience to back it up. So I took the risk.
That brings me to the second point: never lie and promise what you can't deliver. If you can't promise anything, you'll be stuck working with the noobs until you're also not a noob. And if you promise something cool, be confident about it. If you seem flaky, the model will flake.
I have had models want to work with me when I promised them publication on my site and in a eZine. A few were eager to get put onto metal prints and displayed as art around the United States. I offered them something.
No business engagement in any field is ever completely flake-proof, but this is the way to get people to commit and take you seriously as an entrepreneur.
Step 1: Confidently promise something it's obvious you can make good on.
Step 2: Deliver that thing.