Among Friends

[mimomof4]

The Realtor did their job.  No additional gift or money is needed. 

My mother in law was the same way as you and always felt she needed to provide a gift to someone who did a job for her that she paid for (realtor, lawyer, physical therapist, etc)  All these people were already paid for her to provide a service, nothing else is necessary.

Good reviews on their website, yelp, FB, Nextdoor will go a long ways.  People are always asking for references.  Giving this person's name will more than cover what you need.  A hand written letter of appreciation is also appropriate.