Could go both ways...
I am a realtor but I also own a landscaping company and I can tell you first hand that the previous response was spot on that this is "an invoicing nightmare". The Realtors always want it sent to themselves to forward to the client, then they lose it and need it again and again and again... They also have no idea what yard work should cost and if the client is unclear to the realtor or agent and the message does not make its way to you then when the job is done the way the realtor said and not your company than it is still your fault. It is like playing the kids game "telephone" where one person says one thing and it changes a little after the agent gets involved.
If you do take this route make good friends with the Realtor and ask if you can get the clients info to contact directly instead. You always want the home owners info for REPEAT BUSINESS.