Is the index a reflection of the price of sales or the price of bids ? If I go the the store I am told "this is going to cost you $1" not "you set the price by

Is the index a reflection of the price of sales or the price of bids ? If I go the the store I am told "this is going to cost you $1" not "you set the price by buying that for $1" For a real example, read this : http://mechanicalforex.com/2015/01/trading-a-real-market-what-the-swiss-national-bank-taught-retail-traders-today.html http://mechanicalforex.com/2015/01/trading-a-real-market-wha...