Well, it would depend on how they're running the market. I didn't attend the last one, so don't know how it worked.

I imagine, to be completely safe and compliant with RCW 69.51.A they'd have to go through an authorization verification process for every attendee just like cooperatives/collectives have to when admitting patients into their facility.

The law says:

69.51A.060
Crimes â?? Limitations of chapter.
(1) It shall be a misdemeanor to use or display medical marijuana in a manner or place which is open to the view of the general public.

So I'm not sure how having a "public market" would fit under that.