When you collect your car, you will sign a rental agreement. There is a clear section showing any charges due. Before you sign, you must ensure that you are not signing for any items you have not agreed to. With Dollar, once you sign and agree to this, there is no way to refund any charges. Alamo allow you 24 hours after signing to go back to the depot to remove / cancel and extras you might have agreed to.
Typical local charges are for options such as Enhanced Road Side assistance, Personal Insurance, GPS Sat Nav, Child Seats, Upgrade if you request this on collection. None of these are compulsary, and if you see any of these items on the rental agreement, DO NOT SIGN unless you specifically want the option.