Each guild has their very own support system.

The guilds provide valuable services to their members.  You 
get a place to train and study and special bonuses.  These 
services must be supported by the elder members. The guilds  
are non-profit organizations and cannot do these things free. 
Guild dues help support the guilds in which you belong and 
show your allegiance towards them. The dues also prevents 
those who would jump from guild to guild and influence them 
without the trials and knowledge needed to lead the guild in a 
proper way.   Since the guild responsibilities differ, their dues 
are impossible to translate to other guilds. If someone works 
very hard and spends time in a guild they should be more 
eligible for leadership than someone who newly joined the 
guild through a reincarnation. Think of it as if you were a 
map maker and spent years studying the necessary skills and 
supporting your guild. Now you decide you want to be a 
sailor. You couldn't possibly be experienced enough to be a 
ship's captain just because you were a great map maker.

How they work
At level 16 and above in a full level 20 primary guild, you
are charged dues against your guild credit balance.  For most
guilds: it is 1k at level 16, 3k at 17, 5k at 18, 7k at 19,
to 9k at level 20.

Special Dues Systems
Bard, Fallen, Necromancer and Paladin have slightly different
requirements from the above, see 'help guild dues requirements'

Dues Penalties and Rewards:
Note that dues may be lost (and sometimes earned) through other
means than the usual for each guild. Killing members or allies 
of a guild may cause one to lose dues for that guild, while 
killing their enemies may, on rare occasions, earn you dues, as
can doing some quests. This can affect dues for guilds you are
not even a member of, but penalties for guild members are always
harsher than for non-members, and officers may be penalized
more harshly still.

See HELP GUILD DUES, HELP GUILD DUES REQUIREMENTS, HELP DUES COSTS