Do I pay before or after?

As Marina said, you pay Rover for the stay in advance. The sitter does not get paid until after the stay is completed.

You pay and confirm the booking prior to the beginning of the stay.

You pay before but then your $ is held safely by Rover until 48 hours after the booking to ensure everything goes smoothly. If anything is unsatisfactory or there's a cancellation either you or your sitter can contact Rover and you can be reimbursed for any shortcomings or cancellations. I've done this several times for bad weather and I've never had issues with the system. Just be sure to ask for your sitter or Rover for help if its getting confusing!