Aside from what everybody else has said, which is accountability, there’s something else I believe that is very important. There SHOULD be PREPARATION going into the client such a thoughtful program design, scheduling and other communications with the client.
Its unfortunate that in the industry many trainers are not taking the time to come up with an intelligent, thoughtful, safe, progressive and effective program for their clients but that’s pretty much one of the core reasons that they are coming to you, and that needs to be respected. The only real reasons I could think of for a client to not pay up front is because they aren’t committed or they don’t have the funds. In either case when the facts are presented and the client is committed to the program I find that all of sudden things seem to magically work out. ha. Good luck with everything my friend.