I remember a girl asking me for a deposit too, for her safety and to avoid no-shows.
I told her that it was OK using a milestones system. That is a system where you pay an amount of money to someone but it is blocked until you release it on the completion of the service or job agreed. Basically, the money is paid but it isn't in her pocket until she delivers, and you are the one that has the power to release the payment.
She got mad, told that it was insulting her, she couldn't perform well with someone that didn't trust her... bla, bla, bla. I told her to behave or I would report her here and 5 min after ending the call... she had deleted her profile.
The bottom line is payments in advance = scam.