When a model fails to show up or cancels with just a few hours notice this is called flaking. There are several strategies to help reduce flakes. When combined these steps can reduce a lot of flakes, but no method is foolproof.
The first is to check references. People will rarely give out bad references, but if a model is consistently late a reference might acknowledge this. Also don’t just check the references the model gave, if you find photos of the model by other photographers not given as references check with them too.
Another tip is to call the model the night before the shoot just to make sure no grandparents have died, no injurious accidents have occurred, or any of the other common excuses. There’s also something about talking to a person that seems to make for more of a commitment than just emailing back and fourth.
There are also signs of flaking up front. Those who seem hesitant in regards to the location tend to not show up. Also when frequent schedule changes are requested this is another sign the person might flake.
Lastly you can require a deposit. The thought of loosing thirty dollars is enough to discourage many from not showing up because its “cloudy outside” or they have an earache (both excuses I have heard).