In the Marketplace you can trade items and Coins. the maximal number for Players that can be in one Sector is 45
Marketplace[]
There are 5 normal sectors: 
If you dont have Trading-Pass you cant enter the normal Sectors when there more than 30 People if there are less than 30 People you can enter.
Marketplace+[]
There 4 +Sectors: 
for the + Sectors you need too have a Trading-Pass or a Vip-Pass .
when 30 people are in one sector than its full and look like this pic 
Trick[]
There is a Trick too go in full Sectors in Marketplace+
Press TAB and you will see a yellow Quadrad Hold on TAB until it look like the pic
Then Press SPACE and you can go into a full Sector.
*NOTE this doesnt work now