How to join a guild ?
You can join a guild only when the noble title reach Baronet or higher.
Order: guildhall-guild consul-guild list- apply for admission

How to improve the daily amount of purchasing?
There has a purchasing limit for all kinds of goods, you can’t buy this kind of goods any more when the amount of purchasing reach the limit.Unless to invest this kind of goods to increase the favor through the guildhall.
port-guildhall-manager-Yes, I want to vest-choose the goods to invest.
Each kind of goods can be invested once everyday