Editor at Lookout Games
So is it so that you can only receive 4 goods in a single player game, but up to eight in a multiplayer game?
This is correct. However, if you don't like this rule, play with an unlimited Marketplace. This was the original rule. They changed it after people found out that Marketplace is a must-use in solo game and, thus, a pretty dull "strategy". A limited Marketplace makes for a more interesting solo game experience.