During a hyperinflation scenario, volatility will just be bad anyway.
For a non-hyperinflationary scenario, such as we are in right now, if a buyer thinks that they can get the item cheaper in Fiat, they will sell their Monero on an exchange for Fiat, which will pull the price downwards towards a moving average.
If the buyer can get the item cheaper in Monero than they can in Fiat, they will buy Monero on an exchange with their Fiat, which will push the price up towards a moving average.