In EQ, many customers pay extra to unlock better service (game questions, moderation, tech support,...), quests, areas.
I think it would be acceptable for some people to pay to get better service... or it can be in exchange for game money (EQ currency exists... Ebay), experience, or pre-made characters.
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In Shen Mui (sp?), they used a few soda companies like pepsi to sponsor their game. You can buy pepsi cans in the virtual soda can machines.