I've had some of the same experiences, on the few times I placed ads looking for models. My MO was to clearly state on the ad that minors were out of the question, they had to be at least 22 years old and they had to include a picture of themselves in their reply. I then set up an interview with them at a public locations –a rather busy coffee shop. I explained what shots I was after (business images, mostly headshots). If they were still interested we scheduled the shoot. I was open and frank about the shoot taking place in my apartment, except for the one that was gonna take place in a public location (Centre of the Arts).
I had a couple of girls saying they'd go for it and then not even bothering to cancel. One of them, her E-mail addy suddenly went poof. I wasn't in a fit of rage, but was very irritated that they didn't even had the courtesy to E-mail/text about cancelling. (On the other hand, at least they didn't make up excuses: I can't stand liars.)
Yes, many are now suspicious of everything. Sad. However, one thing struck me as odd: there was this one girl –from out of town, actually– who was constantly E-mailing me about doing the shoot no matter what: even when I pointed out that it would not work as I couldn't travel out of town (didn't own a car at the time), she said she had a vehicle and was willing to come to The City to do it. She even sent me several photos of her in sexy poses/outfits. She was asking what kind of photos we'd be doing and what not. I was like, 'what the trout...' Eventually, as it happened I had to rent a vehicle to do a shoot (paid work), and E-mailed her back stating that I would be able to travel to her town and we could arrange something; I also told her the images would be for stock and they'd be about cell phone selfies (nothing glamourous or fashion or sexy). At that point she stopped replying and I never heard from her again.
It got me thinking. I don't want to assert the following as fact, but I still strongly suspect that some of them are actually quite interested in nothing but posing for provocative, naughty photographs. When they're told that the images will be fully-dressed headshots or business-like attire and situations, they bail out. That, if true, is even sadder; especially when many females go endlessly about complaining about being treated as sexual objects. Go figure.