I know I am not the only clinician who has dreaded greeting new patients with a “Hi, I am here to poke around in your mouth and intentionally make you gag. Now, open wide!” The oral mech exam can be a daunting task for your patient. It requires that the patient trust you as a professional. And I do not think I am far off in presuming that this may be a difficult thing for them to do.
So, my advice to you would be to make the patient as comfortable as possible, and have some patience with them. As a medically fragile individual, the patient is doing the very best that he/she can (and that may not always look like compliance).