One way of approaching potential clients is by offering a free session. This will allow for the potential client a snapshot of how the session would go. It can be as simple as going through their routine and fine tuning it or doing a whole new routine with them.
Also, you can offer a free fitness assessment to see how “fit” they really are. Fitness assessment can be something similar to the FMS or ACSM fitness assessment (push up test, three minute step test, etc.)
With your back ground in group exercise, I would target small group training which is cheaper and might be more appealing for the potential clients that are “fit”. The small group training can be geared towards clients of all fitness levels.