How does one tell the difference? The woman I saw last night via backpage ad seemed like a nice, well adjusted girl. No tattoos, no sign of drug usage, she had 2 girlfriends in adjacent rooms. Did not seem traumatized or unhappy.  
Told me she recently moved to Las Vegas from San Fran. However, when I was leaving, I passed a big black guy in the hall who was on the phone and gave me a nod. It would seem as if he were a pimp.  

These guys love them and protect them.. Meanwhile they are taking all their money and giving them some stuff here and there (clothes, drugs.. etc).. Pimps prey on girls who are an easy target or just easier to manipulate (from broken homes, abandoned, abused, with no self confidence, young).. I am not saying anyone else can't be a target but they seem to follow that pattern... Maybe at the beginning stages of the "relationship" they are nice to them and somewhat rational (so no reason for the girls to be unhappy then) but when they start to rebel against the pimp, they get physical, threat them, abuse them verbally etc..  
Pimps come in all shapes and forms.. there aren't really any stereotypes.. but it is well known though, that the majority of them advertise their "girls" on Backpage..

...you're much less likely to find a provider with a pimp. You're highly unlikely to find one being trafficked.  

Thanks