I would say it is different in this case because you only go to those CannaMed doctors for 1 reason- to get your medical marijuana card. Paying for the visit is basically just part of the cost of getting the card. There are no upsells, the doctor isn't profitting off you buying the "medicine", etc. He gets paid for your visit and that's it.
So yeah, completely different than a chiropractor or psychiatrist who profits from your ongoing treatment.
For example, chiropractors often offer free assessments which usually entail an X-ray. I'm not sure how risk-free this is, especially for healthy people in their early twenties. Of course, these assessments usually find misaligned vertebrae and lead the person to go back for a paid visit. Sometimes it's hard to compete with a certified practitioner's recommendation...