RV hosts have the ability to choose how many kilometres or miles they want to include in the rental. When viewing a host's listing and entering your trip dates, you will see how many kilometres/miles are included and what the cost is for extra kilometres/mileage in the price breakdown.

The limit of kilometres/miles per day will be noted, and you can see the cost per extra kilometres/miles by hovering over the question mark icon.
Some hosts choose to offer unlimited mileage, which will also be visible in the price breakdown:

During the departure and return inspections, both yourself and the host will make note of the odometer reading to calculate if any overage charges are due after your trip.
If so, the host will be able to request additional fees for up to 30 days after the trip has ended. You’ll be able to review this request and either accept or dispute it. Note that these fees are subject to a 5% transaction fee.
Please note that the kilometre/mile allowance is calculated per day and not per night. If you are renting an RV for 3 nights and 4 days, and the mileage limit is 100 miles per day, you will be allotted a total of 400 miles for your trip. Any miles traveled over this amount will be subject to the charge as per your booking invoice.