I've posted already on this in other threads, but I was a "Standardized Patient" at several medical schools for 5-6 years, it was a good experience and, at times, good money.
As I mentioned, almost every medical school in California and Arizona uses SP's, several advertise periodically for new SP's to apply (UCLA is generally looking, older males and minorities especially.)
The training tended not to be too strenuous, MOST but not all didn't require too much depth - be able to read a case and remember it consistently (You are Mr. X, have a fever and feeling of pressure in the middle of your chest/back, are/are not feeling nauseated, pain/no pain in arm or fingers. Drink moderately, office job, married 23 years with 2 kids, etc.) Generally just answer the questions they posed, don't volunteer anything extra - make them scratch their heads and figure your diagnosis out.
A few were real acting: you are a battered spouse complete with tears and a (carefully made-up) shiner, reluctant to answer questions - if you can portray one of these cases convincingly, expect steady work.
I preferred the GU workshops some days - being a warm body was no challenge, and I enjoyed the anticipation - sitting and waiting on the exam table for the next group of 20-somethings, feeling the cool exam paper crinkling under my bare butt where the gown doesn't quite meet and looking at the boxes of S thru XL exam gloves and GUAIAC cards at my elbow. Wondering who'd have the smallest fingers, AND biggest; and which ones would bring me up on my toes during the prostate exam (generally the moose with the biggest finger) as they made the plunge. Who'd faint, as happens occasionally (never to me, but several other TA's had stories).
Was good while it lasted, enjoyed the students and their energy, and the campuses are a nice environment. A SMALL part of the reason I stopped doing it was fear of meeting my former students in a session - especially those who got a D in Visual Basic, and might examine my prostate up to their elbows. Awkward to be face-to-face (well, ass-to-face) after hectoring them as a student in a technology class!