I have had a pretty solid relationship with an MMS. In fact she was my regular when she worked the rooms. When she would get a new girl she would tell me to try her if she provided what I liked. If not, she would say she was still a little shy. Once the "shyness" wore off she would tell me it was OK to see her. We never spoke about specific services but she knew what I liked.
If the MMS tells you that she doesn't know what each of the girls allow in the room, she is probably bullshitting you. Although, I don't think many would discuss specifics with a client.