My advice: run her pics through
tineye. I usually only go with the "sexiest one", but if you're feeling froggy run all of them. If even one comes back as not being hers, I pass. Here's an example:
The ad:
http://houston.backpage.com/FemaleEscorts/super-upsc-uty-viab-1-pmt/29825181
The results:
http://tineye.com/search/d38c02be422fe0104c1d91acb4a418 cde141cc9e/
Don't rely on selfies or "amateur" photos as opposed to professional looking pictures to be your litmus test. Camgirls post selfies on their sites all the time and average looking hookers get professional "boudoir" photos done too. Reverse image searching is your best bet.
You can also make some gut-reaction calls based on language. In general, when you see "Outcall Only" you're dealing with a scammer. When a fat, ugly or pimped girl shows up at your house or hotel room, what are you gonna do? Kick her out and risk a scene at your home or hotel where you are registered? Not likely. Besides most guys are stupid and will fuck the uggo that just showed up anyway.
But to answer your question, no. There is no surefire way to weed out all the bullshitters on BP. If that turns you off of using it as a hobbying tool though, you're missing out on a pool of new chicks who are trying to get themselves established. I've found some really hot hookers who perform off of there. It's not often, but they're out there.