Your clients' "gym experience" is based upon the environment... the facility, the energy, etc. Their "trainer experience" is based upon your interaction... your people skills, the quality of customer service provided, the degree and quality of attention you give them, etc.
But the "Exercise Experience" (or at least the portion that you can directly affect) is based upon sensation... what it "feels" like... each workout... each exercise... each REP!
And it's not just a matter of exertion. Absolutely anyone can make exercise "harder". The question is can you make it feel extraordinary?!
This can mean many, many things. Can you make an exercise more challenging in a very specific way, rather than just generally strenuous?
When someone has knee pain, do you push through it or avoid exercise altogether? Both options can be less than ideal.
The skilled manipulation of the variables of Exercise Mechanics and the use of intention-based instructions empower you to create experiences that your clients' can't create on their own and won't find anywhere else.