called "pay-to-win" (abbreviated as "P2W"). In general a game is considered pay-to-win when a player can gain any advantage over their non-paying peers. Market research indicates that pay-to-win mechanics are considered much more acceptable by players in China than in Western countries, possibly because Chinese players are more habituated to recurring costs associated with gaming, such as gaming café fees. A common suggestion for avoiding pay-to-win is for payments to only be used to broaden the experience without affecting gameplay. For example, some games, such as Dota 2, Fortnite Battle Royale, and StarCraft II, only allow the purchase of cosmetic items, meaning that a player who has spent money on the game will still be on the same level as a player who has not. Others suggest finding a balance where a game encourages players to pay for extra content that enhances the game without making the free version feel limited by comparison. This theory is that players who do not pay for items would still increase awareness of it through word of mouth marketing, which ultimately benefits the game indirectly. In response to concerns about players using payments to gain an advantage in the game, titles such as World of Tanks have explicitly committed to not giving paying players any advantages over their non-paying peers, while allowing the users buying the "gold" or "premium" ammo and expendables without paying the real money. However, features affecting gameplay and win rate, such as purchasing a 100% crew training level, a premium account, premium vehicles, and converting experience points to free experience points, remain available for the paying customers only. Play-to-earn Play-to-earn, also known as pay-to-earn, is a model of monetization that uses cryptocurrency and other blockchain technologies. Nagging In single-player games, another concern is the tendency for free games to constantly request that the player buy extra content, in a similar vein to nagware and trialware's frequent demands for the user to 'upgrade'. Payment may be required in order to survive or continue in the game, annoying or distracting the player from the experience. Some psychologists, such as Mark D. Griffiths, have criticized the mechanics of freemium games as exploitative, drawing direct parallels to gambling addiction. Purchases by children The ubiquitous and often intrusive use of microtransactions in free-to-play games has sometimes caused children to either inadvertently or deliberately pay for large amounts of virtual items, often for drastically high amounts