The rebate agent is being paid the same way as any real estate agent in a real estate transaction. The seller typically puts up 5-6 percent of the sales price to be split between the listing agent and the buyers agent (rebate agent).
Depending on the commission split percentage, the rebate agent will generally accept 1% as their commission while rebating the remainder of the commission to the buyer at closing.
Discuss with your agent if there is some detail that you are unsure about. Work out the details of the type of services you need from the agent, and acknowledge how your agent is being paid and how you will be getting a buyer rebate at the same time.