Yes, I believe it is a racket. The hotel I stayed at gave me folios when I checked out and the price of the rooms booked through AAdvantage were significantly less than what AAdvantage charged me. The taxes did not add up. I called AAdvantage and they said that the hotel was not supposed to give me the folios because it showed the contracted rate that AA has with the hotel and that the price difference is the commission that AA makes. I asked why AA charged me taxes on their commission. They had no answer. but, this might explain the different tax rate you saw. If they are charging tax on the commission, it could be tax in a different state/different rate. Needless to say, I will never book through them again.