IMHO you really need to be careful of the ones on BP offering outcall only.
Unless you have a really solid recommendation you should avoid.
I personally think a lot of the scammers only do outcall because they know it is easier to rip guys off.
It is one thing to show up at her door to find out she is nothing like advertised and be able to walk away but if she is at your place or hotel, it can turn into a bit of an dicey situation. They know most of us don't need some big scene on our front lawn or in our hotel room so we'd rather quietly pay them to go away.
Be very careful arranging outcalls with someone you are not familiar with.
Cheers