This is a horrible idea and here is why:
IRL market this work because there are a limited amount on both supply and demand on reality.
In FF14, the supply of gil is relative low (quests, DR, challenge log, in short: the world "print" money slowly) but the goods have an infinit supply and its fast (gathering, then craft them)
So an offer board will cuz: no buyer will ever buy things from the current MB, they want something they will just search the current MB for price then post an offer with lower price.
And then RMT and BOTs will pick 99% of these offer before normal players can even react or borther to react due to super low price 24/7, this will completely crush the economy as normal producer will not be able to make gil. So the low end stuff will be trash vender value and high end stuff will be super expensive cuz RMT will sell more gil which will raise the inflation.

As long as a bot can gather 800 logs per hour this shouldn't be introduce to the game.