She could have been tipped off by Sol on what was happening and as you said this was her way of abstaining,Another fantastic tribal council and another blindside.
I don't understand why Rachel would use her Shot in the Dark when she had an idol though. Could it be that she was well aware of what the plan was (i.e. either Sam or Ciara) and didn't want the survivor of the vote to turn against her later, so it was her way of abstaining from the vote?
And/or it was a way of reading the reactions of people when she played it, and she got a bad vibe then she could have played her idol. "Shot and a Chaser" I heard it referred to.
I enjoyed this Auction more than the one in 45. I think they fixed a lot of the issues it had by putting in the cashback and other activities.