All I have to say is you get what you pay for or if you pay too little, you get what you don’t want to pay for as well.
Be honest with yourself and your employees. If you are paying well, you can expect a little more effort from the trainers. Say so up front, as in “I am paying you 25% more than the area market. That is because I expect everyone to pitch in on keeping the gym clean and tidy. And always be professional”. Put it in writing what the pay is and what the trainer’s duties are going to be.
There are a lot of little and big perks that you can bring in later if things go well. Like in house CEC programs and bonuses.
And a little note on the side. Years ago I worked for a gym owner who paid me a reasonable amount for that time and location of the gym. But after two years, they didn’t want to give me a raise. I was a little bent about it. Then I figured out how much I was bringing in for them and realized that I brought in 5 times what I was paid. They owned three homes, boats, cars, and were opening other businesses. I asked them to let me pitch a raise again and they said “no”. So, I left and opened my own place. I made twice as much take home the first year and never looked back. They never got anyone to stay in my job for as long as I was still in the area. And the ones that worked for a while and left only brought in a fourth of what I was bringing in for them. I was happy with the job, but not with the inequity of what I produced to my income. That is how this industry works. If you have a good employee, pay them well or they will just take their hard work out and open their own gym.