Converting a 20 USD Play Store gift card to cash is an idea that some people may entertain. However, it's important to note that Google Play Store gift cards are designed for use within the Google Play ecosystem and not intended to be directly converted into cash.
The official stance of Google is that these gift cards are for purchasing apps, games, movies, music, and other digital content on the Play Store. Any attempt to bypass this intended use and convert them to cash goes against the terms and conditions.
Moreover, such conversions are often associated with risks. There are many unregulated and potentially fraudulent platforms that claim to offer this service. These platforms may not be legitimate and could lead to loss of the gift card value or even expose users to other security threats like identity theft or financial fraud. It's advisable to abide by the rules set by Google and make the most of the gift card within the proper context of the Play Store.