Although the rates and taxes information might be provided on the property listing or property brochure, in cases where it tends to be on the high/low side, the agent will be able to provide you with more information as to why it may be high or low.
Perhaps you as a home buyer aren't used to seeing such high utility costs, especially if you are moving from a smaller home, or a sectional title unit into a larger freestanding property with a possibly larger erf.
Always remember to ask this question, as it will be a shock to the system if you get your first rates account after registration and your budget was not adjusted to accommodate this additional expense.