Super good question.
Although these are active customers, they might not be active for the next client, since so much of your business is YOU. Unless your clients are tied into contracts that they haven’t paid for yet, they might not like whatever trainer buys your client list, making it worth very little.
If it were me, I’d package it as purchasing your client list and shadowing your sessions for 2 weeks to transition from you to the next person. If you find a good trainer who has a similar philosophy and training style as you, who could step into similar shoes / qualifications, the list might be worth a lot. You’d be selling the client list and the transition. That’s going to make your list worth a lot more because people will be more likely to stay on with the new trainer.