To be honest, I find Backpage to be a red flag all by itself. If I can't a find reviews for a provider advertising on Backpage, I assume the experience will be disappointing. NCNS, high volume, bad attitude, upselling, short time, bad hygiene, etc.

But the biggest red flag is when some of the pictures don't match the rest. Like they are pictures of two different women. That makes me think that at least some of the pictures aren't her, and maybe all of them. And she is probably using misleading pictures because she doesn't look good.

All that said, I did see a provider several years ago who had mismatched pictures, and had a good time anyway. She was on Craigslist, but that's basically the same as a BP ad today. Her pictures were of a hot, slender latina and a similarly hot white girl with dark hair, but in person, the provider was a nice-looking native american woman who was a little on the thick side. She was really nice and the sex was good.

or tineye to reverse image search to see if her pics have been used in different ads

If the pictures either look like a civilian 10's pics off her facebook (all clothed) instead of pro's pics taken in lingerie in a hotel room or bathroom... or if they look like professional grade model pics... AND especially if the price is then named and is below market (GFE for 120 or whatever)... well too good to be true generally is NOT true

No ter or p411 references. Or at least a website/social media presence.  
Basically stay away from ads with just pictures and a number.