My sense is that the ones who simply say "Hello" or similar are professionals looking for clients.
I've had three relationships through SA, each of them DDG to these eyes. The first, a 23 y/o French grad student, asked for a gift as a show of good faith. We met for dinner, I gave her an art book, which totally blew her away. We had dinner twice more, two more dates at my place before she put an end to it, clearly uncomfortable with the concept. She's only logged in once (at least as of the last time I looked, about 10 months ago, to remove her picture.
I also met the second, a 26 y/o Quebecoise massage therapist (not erotic) for dinner, consummating the relationship, which lasted three months, on the second date. She asked for nothing for the first meeting. Also a non-professional, she'd a prior three year SD/SB relationship which I ended shortly before we met. While she was gorgeous, we really had nothing in common. I've gotten more pleasure from most escorts I've met.
I also met the third, a 30 y/o artist, Anglo-Canadian, for dinner, for which she also asked for nothing. After dinner, we took bixis downtown to the Jazzfest, before walking back up to the Plateau to our respective homes. We met once more for dinner before consummating the relationship, which is now in its second year. I give her a weekly allowance and we have sex once a week, a date which can run anywhere from 4-8 hours depending on what else we have planned; she only occasionally spends the night. We often meet for a concert, brunch/dinner, or a movie on another day as well. We've been to New York, Berlin and Prague, and have two more trips planned in the next three months. If I'm gone for an extended period, I still give her the allowance, though if it's only for a week or so, we'll have two "paid" dates either immediately before or after my absence. The only time she doesn't get her subsidy is if she's out of town for a while. I dare say this is the most satisfying relationship I've ever had with a woman. We are extremely fond of each other and we are also extremely fond of our individual freedom.