I've been on both sides of this.
Most trainers have always been fit. I haven't. At my heaviest I was close to 100kg and 35% body fat — the wake-up call was a photo of myself in swim shorts.
A pageant once gave me five weeks to get on stage. I refused to starve my way there — I built my own programme, kept eating properly, and walked on in the best shape of my life. That programme is the foundation of everything I coach.
Since then it's been stress-tested: coaching undergrads to 60-something professors at NTU's NorthHill gym, training through a full-time Apple job, a slipped disc, and a knee and shoulder injury. Not harder — smarter. It kept working.
The clients I care about most are the ones other trainers gave up on. That's the whole reason cubbytrains exists.