What a fucking disaster this is on so many levels. Although this is an imaginary line, if or when it's crossed, it could become a major problem. The zoo animals at this point are now running your show.
It's true that personal training is in part about developing relationships, but you have to be careful how the relationship develops. The main objective is always about the goals of the client, and what you will do to help them achieve them, not the other way around.
As a trainer, it's imperative to set the tone from the git go, otherwise you've already exposed yourself as a weak leader.This is about boundaries and certain lines that shouldn't be crossed, and if so, it MUST be consequential on all sides.
It doesn't mean you can't have fun, because part of a personal training experience should be a vibrant atmosphere that creates a unique vibe. A legit trainer is always mindful of this, along with providing the client with cutting edge information especially regarding the three crucial training components.
Just as important to this dynamic is the environment that will be anything but boring, in fact purposely designed to make each training session interesting, thought provoking, even a bit inappropriate, or at least awkward for the sake of a great training session.This is part of your gig as a trainer who brings something special to the table providing your clients with something they can't get anywhere else.This is job security baby!
Keep in mind, this imaginary line can be a tricky one if and when crossed, but a legit trainer will at times push the envelope, knowing in order for a client to stay motivated, and dedicated to keep showing up, it has to be much more than an average training program. Trainers to a degree can become a buddy to their client but never at the expense of losing control of the relationship.