I never refused to send deposits. Actually, I sent one to the first SP I met, even though she didn't ask for it

. Meeting her was a big deal for me and I wanted her to know that I was serious. Its easy for a client to check if a SP is for real. MERB's reviews, Montreal Indy Companion website, the quality of the SP's website and sometimes, I use the Way back machine to check how long the SP had a website. Mind you, I only see Independents. If I were to see SP's from LL or other no so reliable sources, I would be very cautious.
I think it should be routine that if you do not have a reference from a wellknown provider, you should expect to send a deposit. After all, we are not paying months in advance, usually it is a few days before the actual encounter. I believe the likelihood of a new client cancelling or worst yet, not showing up is pretty high if he refuses to send a deposit.