with about 90% of the agency's out there the pictures they use are fakes, if you cant find them on here they are more than likely fake.  

In some of those cases they use different names when working for the different agencies. So your scenario can be considered common. Sometimes it is legit, and sometimes it is a B&S or scam. The key is doing more research. Look for reviews (of the gal and the agencies). Ask about them on your local board or search. The fact that two agencies are using the same pics with different names is not a red flag to me, but I would certainly want to know more.  
If your research concludes the agencies are legit, and the gal is legit, and you still want to book her, then you have the option of going with the agency that charges the lower rate.
(I actually don't know if one is cheaper than the other, but it happens and that is the kind of thing you find out doing research)

One of those agencies has many, many good reviews that say "real pics". I only found one review for the other agency that said "real pics".  None of the reviews are  for your Farah / Gabby so the verdict is still out