I assume you are talking about personal website ads. I have seen many such websites that have links to "friends" or "I do doubles with" links to others' Profiles.  

"Friends" are very often Providers in the same "category" (similar rates, similar touring, similar services). If you like Mary, then you might like her friend Susie. And Susie has a "friends" link back to Mary. (Damn: there's a word for the whole links to each other in a ring, thing.) Some "friends" links are just placed there via a consolidator and the girls might not really know each other personally.  

I have seen websites that provide links to other Providers that the do doubles with the Primary. Duo claims usually sounds more legit and real, to me, and the girls have probably (but not always) met under intimate circumstances.

But the primary Provider usually has a Profile. If she has NO PROFILE (yet), it is reasonable to assume the friends and duos claims are legit but, as far as they go, they are not as reliable as TER reviews. If a duo partner is well reviewed, you can ask her if she really does duos with the non-Profiled primary but that's getting a little sketchy and she might consider you a time waster.  

Exactly who or what ad are you talking about?  

... and thus there's two (in this case) names on the profile?  

There was a case on the Photo board late yesterday in which the handle under which the post was made used the provider's old stage name, but the name in the subject line was the new stage name.  The profile has both names. Additionally, the email for contact embeds the old stage name while web sites refer to the new stage name.  

I could see where that could be confusing, if that's the kind of thing you're referring to.  

It becomes clear once you read her reviews and see that at some point the stage name changed, thus the profile is in fact for one person, not a provider and her girlfriend. There are profiles with duos, but those are easy to spot because they're under "ProviderA and ProviderB".  In the case of a name change, a "/" is used between the different stage names... two or more.

providers" but also may indicate possible doubles partners, depending on any additional wording.