I work for a human services company and oversee the support of one of our elderly clients. A coworker is leaving the business to set up her own, has offered me a position, and wants to land the aforementioned client. She knows that due to my relationship with the client's guardian, she would be unlikely to land the client without my association. I plan to leave our business as well (but don't want to work with her) but would like her to pay me for giving her business a positive recommendation to the client's guardian. Is this illegal? Can I put our agreement in a contract (she won't be able to pay me unless she lands the client)?