Quizcover comes with a Booster Back guarantee: if you use boosters on a question and those boosters were deducted from your account (not just "free" boosters), you get them back unless you score at least some points on that question. You can then use them on some other question.
This relates specifically to boosters, not to other purchasable interventions such as retries (which are like renting a tennis court for an additional amount of time) or the immediate activation of bookmarks.
The Problem This Mechanism Solves
The founder of the company that developed Quizcover was frustrated by the way some other games, especially (but not only) games in which the primary objective is to advance to higher levels, essentially force gamers to throw good money after bad because all boosters spent on a level are lost if one doesn't achieve the obvious goal of reaching the next level.
Whether you actually paid for the wasted boosters or earned them (such as by collecting daily free boosters), it's frustrating if your boosters feel like a waste.
Quizcover can't always know what objective a player has. For example, someone may want to set a new record superstreak or defeat a rival in a duel. Since the game can't read your mind, the Booster Back guarantee can't relate to such hard-to-identify scenarios. But if you don't score at all, despite using one or more boosters on a question, then the game definitely knows that you didn't get what you hoped to achieve, and in that case it automatically refunds those boosters (not in terms of giving you coins but in terms of you being able to use the same booster(s) on another question of your choosing):