If a lady is traveling for an appointment with a specific person, and even with a tour, there is always the risk that something will come up. Weather problems can delay flights. She could get ill. If she has a child, she might not be able to arrange someone to watch the child. There could be a death in the family. Or, even simpler, the girl may have a shoot that day that she didn't know about when the date was made and needs to do the shoot. There are always legitimate reasons.
There are also flakes. No one has flaked on me. But, if you search this board, you'll find postings about porn stars who flaked on a date. That happens too.
One of the reasons why I like dealing with agencies, is that if you have a good relationship with the agency, and the agency is an honest one, the agency will steer you away from girls who flake on appointments. And, if the girl flakes, or has a legitimate reason not to make the appointment, the better agencies will "make it right". That could include everything from rescheduling the date, offering a replacement, offering a discount or something else.
Frankly, the better agencies won't consider their responsibility ended when they tell the girl to show up. The better agencies will book the flights (if needed), arrange car service (if needed) and will continually remind the girl about the date and keep in touch to find out if there's a change in plans. IMO, if you're dealing with an agency who thinks their job is over when they tell the girl about the date, then you should look for another agency to deal with.
The agents and the girls are in it to make money. They don't make money by flaking on dates. They don't make money if word of mouth on sites like this is that they flake on dates. They have every incentive NOT to flake. And, like I said, the better agencies will not flake and will not let the girls flake. But, shit happens. And, like I said, the better agencies will make it right because they want you to come back and use them again. You won't do that if you walk away unhappy