Yeah, that has to be one of the most frustrating thing in dealing with models. If it's not what you described, it's the whole barter game back and forth. They turn it down, then a day later blow your phone up because they've changed their mind.
Another is thinking you are like Vivid or something, and going to 'contract' them so they can quit their job. I love how models tell me, "Wow this is easy money. If I could do this a few times a month I would quit my job". I always advise them against it.
