Hiya Jo
i actually work for the agency, and yes the initial visit is difficult for both child and sitter but if you sit for the same family on a regular basis then its not a problem...
i love my job and the children that i look after and i know that lots of my families find my services invaluable. I do undersatnd your apprehension though after all our children are so precious we wouldnt want to farm them out to any Tom, Dick or Harriet, or let them into our home for that matter!