I have asked for a token deposit before off a client who cancelled on me twice before that, as a show of.good faith for holding the booking. We are talking a £10 deposit though, nothing major.
Also, like Charissa I would in theory travel for longer outcalls but if the train fare/time taken is a lot, I would expect travel costs to be paid up front by a first time client. I have done this twice and because I have asked for travel.costs only, clients have never had an issue with it.
However, asking for a deposit up front for a regular booking 9 times out of 10 seems to be a scam to me.