You will need to find the administrative office for your region and probably visit it to get through to the manager. My PR course was in the Bay Area. The main office is in Palo Alto and the manager had strange hours so he could be reached by email. . . Once you find her/him you can ask for the names and qualifications of the instructors and how long they have been running that course. . . they will tell you all of the instructors are awesome.
you will need to do some word-of-mouth searches to find STUDENTS who were in their classes. Preferably hard-working students vs complain-about-everything-and-never-do-the-homework students. This can be very hard to do.
I would warn you that obtaining reliable information could also be difficult because of how these courses are staffed. The schedules are set in stone months in advance and sometimes there are conflicts with instructor availability . .. leading to last minute changes in staff to fill the course schedule.
IMO: While the instructor is important to guide review of the material and for answering questions about Hw/passages YOU will make the most difference in this process. I had a great Physics, pretty good chem/ochem and a silly bio guy while my verbal guy was smart but useless since the PR verbal strategy was not useful for me. I did great, got a 38 after that inhuman effort.
. . .The MOST I got out of my prep course was the structure, the resources, and above all keeping up with the homework schedule while completeing all the practice tests and additional online passages.