Which of the following is an example of reciprocity?
a. A real estate agent refers a client to a real estate attorney, and the attorney recommends a contractor to the same client.
b. As a wedding planner, you recommend that your clients hire a specific DJ service, and they refer clients to you.
c. In response to the shortage of used vehicles, the trade - in value of your car increases.
d. A customer service representative provides excellent service and you rate them a "5" on a customer service survey.