It depends on the slot for sale.
Slots that were purchased by members, during members-only registration, are only available for sale to members.
*IF* no member buys it, then it would be available to the general public.
Slots bought during open registration are available for sale to anyone.
Since all matches so far have sold out during member-only registration, you would need to be a member to buy the slot.
At least this is my current understanding at this time, based on discussions with Jim See and some of the MDs.