Hi CG,
The first step is not to let this get to you. Difficult at times I know but it will only eat away at you and affect any other bookings you have planned and could totally effect your business.
Unfortunately, anyone that has ever done an outcall booking will know, nothing in this business is guaranteed, not even those ones that you have done a complete security check out on. If they decide to not open the door you are screwed in the wrong way.
This is the reason why some girls insist on a deposit consisting of travel both ways plus a little extra for you travel time and that way you don't feel QUITE so bad. Of course everyone hates having their time wasted and being made a fool of but that is a chance we take if the correct procedure is not carried out.
Sorry this has happened but if you ask for a deposit and they are reluctant to pay then this is one sign they ain't serious. Not the only reason but one of them and if it saves you wasting your time then something good has come out of it.