Online “dark nudge” services -- free trial subscriptions -- are rattling South Koreans who end up paying fees they do not anticipate, according to the consumer agency Monday.

A number of online services, such as music and media streaming sites lure consumers by offering trial subscription and automatically charge the users for the service after the period is over. This small “nudge” of free trial periods are used by businesses targeting consumers who are not very careful about reading the terms of agreement and lead them to involuntary purchases, the Korea Consumer Agency said.

According to agency, a total of 77 such complaints were reported from 2017 to October 2019.

Among the reported cases, 49.3 percent of them complained of the difficulty in terminating their subscription after the end of the free-trial period. Over 44 percent cases were on how the companies charged them without giving prior notice, after the free-trial period ended.

The KCA said it has reviewed 50 applications that offer trial subscriptions on Google Play Store and Apple App Store and found that only 26 of them asked for prior consent to convert to a paid subscription.

Even if the service providers ask for prior approval, consumers often forget the exact time they need to renew the contract, the agency noted.

Only two out of the 26 applications sent a notice three days before the free subscription expiration to alarm users.

The agency said it will recommend regulation revisions to the Ministry of Culture, Sports and Tourism to guide companies to notify users of such subscription changes.

By Jo He-rim (herim@heraldcorp.com)