"First I would introduce myself and ask you how you've been enjoying the gym. I would also ask you had a fitness goal in mind that you were working toward. If you had a particular goal or were training for something, I would let you know the services I offer and tell you a little about my experience training athletes. I think it's important to build trust with potential clients and make sure that I can help them achieve their goal before I try to sell them sessions. I may even offer a free trial session to make sure it's a good fit."
Walk your interviewer through a hypothetical conversation with a future client. What types of questions do you ask them? How do you gain their interest?