That's what I do - if there's a number I call, ask a few simple questions and generally get the feeling if she's ok, confirm a time, and call or text when I'm there - simple really - few mins at the most.
If email then it's typically the same and then eventually the girl gives you her number so you can call or text when you're near. It's never been a problem but I do understand, from talking with the women, what goes on and what it can be like and some of it is not good. A booking, in some way, helps prevent timewasters I suppose.
There's a lot of guys who are genuine - and a lot of women who are genuine but like everything else - PG scams, setups, thrill seekers etc - there's always those who will try and abuse it for some reason or another.