The US Federal Trade Commission is planning a review of the marketing and delivery of products with in-app purchase capabilities through Apple’s App Store, according to the Washington Post. The move apparently stems from the fact that customers may not fully understand the new payment model, following earlier concerns that children have run-up large bills through in-app purchases, without realising that money spent in games or other apps is “real.”

In addition to the Washington Post’s comments on the US market, the BBC has run similar stories in the UK, including the example of a child running up a bill of almost £500 on in-app purchases. It reported that seven free products aimed at children did not clearly warn the user of the potential to spend real money from within the app.

The news follows shortly after it was reported that US and EU regulators are eyeing Apple’s subscription purchase strategy, focused on the company’s practice of “funnelling” content through the App Store in order to ensure it can take a 30 percent cut of the proceeds. This followed the blacklisting of a Sony eReader app from the store, because it linked to the company’s own content store.

The investigation is especially significant as in-app purchases are becoming an increasingly popular way for developers to monetise products – the initial purchase can be offered free-of-charge to create a large user base, before charging for additional features once the value of a product has been established.