You used to be able to create a sale item that clients could buy as a deposit, but now you can only use sales for physical items that can be mailed. You could do it by setting up a phone or webcam booking which doesn't actually happen, though.
I mostly use amazon for my deposits. I get them to send me a gift certificate and just have the credit in my account for whenever I need to buy something online, since they sell almost everything. It's not actual cash of course, but it's safe, quick and fee-free.
We'd talked about other ways to take deposits, so search if you're interested.