10 March Helpline Q&A When experts are the subject of regulatory complaints Fitness to practice, regulator, 16. Criticism and Complaints, Professional Body Most professionals who act as expert witnesses are potentially subject to fitness to practice or other types of regulatory or professional body investigations. This can be extremely stressful and challenging even when the complaint appears to be vexatious or lacking in substance. So, we thought it would be helpful to offer a brief reminder of what you should do in such circumstances to ensure you meet your duties as an expert witness.