Visitors to the Habbo Hotel (mostly young teenagers) don't pay to enter, but the economic model requires that users become sufficiently engaged to buy both low-cost items and access to paid areas to improve their experience. The marketers at Habbo have been very inventive in finding ways to get teens to try out the purchasing experience and making sure their parents are happy with it, too. Marketing Sherpa interviewed the marketing team at Sulake, based in Finland.
MarketingSherpa: How to Get Teens to Pay for Virtual Content, 2006-Aug-18 (paid after August 28) ($5 article)
They used the scratch cards at promotional events to distribute coins to give teens a taste of what they could do in the Habbo Hotel, like iTunes giving away a song. Habbo recently tested a $10 prepaid card with CVS. The card had to be swiped at the cash register to activate... “we set a limit purposely on every payment method, anywhere from $20 to $30 per payment method.” .... Habbo quickly reacted to any problems with parents upset over their children charging payments without their permission, offering partial refunds and banning teens from the site for periods of time.