Most of the trainers you will talk to they prefer to get paid in advance. Of course there are some who charge their clients after a certain number of sessions have been performed. The reason trainers like to get paid in advance is that their time is as valuable as their client’s. And when this option is the preferred method of compensation there is usually a cancelation policy in place as well (usually 24 hours).
You can search online for trainers in your area and see what kind of payment requirements they have in place. If you approach a company that has a number of trainers under them, you can request a different trainer if you wish. They all have policies which you can read and sign if you agree to hire them. Check for testimonials, Yelp reviews, etc. before hiring a trainer or a personal training company to make sure this is the right fit for you.
As Ariadne said, IDEA is not a personal training company but you can search under the “fitnessconnect” section for trainers near you. I hope this helps.