I had one this week on the phone. A few months ago I agree to a listing in a contact mag that you can buy in adult shops etc. (AFAIK), and he was the second caller to mention it - when I referred him to my website as he was asking a lot of basic questions: he said it was difficult for him re. anonymity. He sounder older and I suspect it was more technophobia.
Anyway, he just kept going back to asking what I would be wearing. I explained that especially if he booked 1h+, I'd try to accommodate any specific requests, that I had various babydolls, lingerie etc., and a couple of PVC dresses. He then wanted to know more about the latter, and which one showed off my figure etc. I genuinely had to go and get ready for a client so I got rid of him and told him to call when he was ready to make a booking. I don't think he was wanking at the time, but just generally came across as pervy.
Tl; dr - asking too many specific, personal/detailed questions.