Please be aware that I’m not responsible for any impact of this article to your Google account. And it is tested on some paid applications (can’t tell you the applications sorry).
There are some applications that lock premium features. To unlock them it needs you to buy or subscribe the service. So how to manipulate the subscription? Of course you must first subscribe (via Google payment gateway). And fortunately Google allows us to cancel your subscription between 30 minutes (it maybe has been changed now). Some applications only check the payment status and unlock the premium features right away if it was successful but don’t detect if we cancel the subscription between the time, and yes Google do refund your money and you still can enjoy those premium features for free. So between 30 minutes after you do subscription is your golden moment to manipulate it and see whether the application algorithm is good enough. My suggestion is to have a one year subscription and cross your finger. Good luck!