The notion of selling extra tickets at face value isn't as clear-cut as people make it. I've sometimes had extra tickets to things and have sold them on StubHub, Ticketmaster, etc., and many times when you DO resell something for cost+fees (so that it costs a bit more, but after they take their piece, you break even), I would say at least half the time I did that, the ticket was purchased immediately and then reappeared on the site 10 minutes later with a huge markup.
Even if someone posts on here that they have face value tickets, there is no assurance that that person who grabs them won't just resell them.
So, the notion that ticket buyers should all be on the same side doesn't have any real safeguards. Brokers could monitor this site for tickets pretty easily.