I've seen a lot of bug reports about the GBT, I'd like to sum up those

- Make sure to always display at least one bid and one ask,
since the game doesn't display all the available trades, some ressources cannot be bought or
cannot be sold (maybe, for each ressource, have one page to buy and one page to sell)

- Allow to buy / sell partially, i.e. if someone only wants to buy 100 ores and there's a trade to buy 1000, he/she
could buy 100 ores and the 900 remaining ores would still be available (you can just remove the
1000 contract, and create a new one of size 900)