a personal trainer who does not know what they are doing or isn't very good. They are not real personal trainers but rather people who count repetitions of an exercise. The best example of a rep-counter is a trainer who places their clients on a series of machines, demonstrates the form for the machine and then proceeds to count reps. Since most people are capable of reading the printed directions on the machine so this activity is not really personal training but rather "rep-counting."
Man that personal trainer is making all the good personal trainers look bad! They just put their clients on machines and just sit there watching, what a rep-counter!