Hi Jennifer. Great question! I echo some of what Susan has said here (e.g. perform your own assessment, have a short “getting to know you” meeting to go over their goals, your style of training etc.). But after this “initial meeting,” I’d start putting your own stamp on their training sessions immediately! After all, you are NOT a “substitute” here, and unlike let’s say a substitute teacher who simply carries on with the “regular” teacher’s lesson plans, you ARE now the client’s trainer. I wouldn’t necessarily make a full training change overnight with your client, but instead follow some of what the former trainer did (to the extent that you agree with what they are or have been doing) and mix in some of your own exercises/philosophies. Then, as each session passes, don’t be afraid to start weaning the client off of their old program by including more and more of your own. Before you know it, the client will be looking forward to the new challenges that you bring, rather than lamenting their old program.