Online Marketers are people who recognize the need for multiple income streams, but many miss the opportunities to expand their business, that social networking sites afford them. These sites can be used, but you must take care not to violate the rules set by the site admin.
For example, Tim is an online marketer who sells posters of bands. He has set up a profile on Facebook.com and joined a group of fans of the band AC / DC. In messages he noticed someone asking about the poster on his profile page. He messages back that he has an extra one and he is willing to sell it for X $. Tim makes sure the friend knows it a special price just for friends. The friend buys the poster and Tim ships it to them.
When using a social site you must remember the site was designed to find people with common interests who may become friends. The terms of service have no problem with one friend selling something to another friend, but I suggest always messaging to said friends after they buy, so they remain your friend and, as we know, once a customer they are possibly a repeat customer.
The key to this transaction is, it's a friend selling a poster to a friend. This requires the art of Selling without looking like you are selling. One mistake to avoid is sending a group message offering posters for sale. This action constituents SPAM and we already know what they do to SPAMers.