Charging money also makes the person value the interaction with the community more so they will be less likely to trash it since they are investing in it. On the other hand, since they are paying money for access, they might claim "It's not my problem," when problems arise since they might expect the person they are paying to deal with the problem. However, if you make the AccessFee low enough, the fee might feel more like a low key membership fee (say to your local legion) rather than a ticket for entertainment.
Needless to say that once you start charging money, you become responsible to account for that money. Starting a NonProfit corporation may be a prerequisite, but that will not only increase overhead, but it will increase the bureaucracy and pain of having an OnlineCommunity. Also, one will need to build the infrastructure to collect money. This may be as simple as having people mail you cheques, or it may be as complicated as acceptng credit cards electronically. A typical compromise is to use PayPal, but even that requires some work.
Thus, one may not want to charge money until a community matures; i.e. until it has enough pain that it seems necessary. Coupled with the need to build momentum initially in the CommunityLifeCycle, it probably is a good idea to wait.
Exchanging money is also complicated for the end user, as he or she will either need a credit card, a PayPal account, or need to physically mail a cheque to the host. For certain classes of people, this is impossible, especially college students or people in far flung countries. You may want to create exceptions for these people if they are intrinsic to your community, or may simply want to create two classes of citizens. The latter solution may simple reflect existing ClassStriation in your community, which is probably a bad thing, but maybe useful in certain circumstances like communities built around elitism (e.g. a golf club).
Charging money can be structured in a variety of ways. One could create a contract for services that two or more parties may sign. One can put money in escrow that may be withdrawn only as a penalty for misbehaviour. However, a very simple and effective method is to charge money for access.
There are two principal ways to do this. Magazines reflect both.