I can see where you might accept a specific lady who happens to work for an agency as reference, you could at least check her reviews and know a little about who is giving you the OK. What do you really know about the agency? Your putting your trust in the OK of an organization you know little about, basically accepting them as a valid screen without knowing their procedures or if they really know the potential client and that he is OK. I could see some ladies accepting an agency on a case by case basis if they knew a lot about the agency itself.  The ladies I know would have a hard time accepting even a direct agency girl as a reference. While it has been recommended that newbie guys can sometimes get started with agency girls as its easier to get screened, what often happens is they still have no reliable references for other ladies unless one of the agency girls goes independent. In the end the risk your willing to take is up to you that is why there are no hard and fast answer to newbies about references, each lady determines for herself what makes her feel safe.