Bundle (in which a portion of the sale is given back to the publisher or distributor), distributed as part of a physical release to redeem the game, or given to a user as part of promotions, often used to deliver Kickstarter and other crowd funding rewards. A grey market exists around Steam keys, where less reputable buyers purchase a large number of Steam keys for a game when it is offered for a low cost, and then resell these keys to users or other third-party sites at a higher price, generating profit for themselves. This caused some of these third-party sites, such as G2A, to be embroiled in this grey market. It is possible for publishers to have Valve to track down where specific keys have been used and cancel them, removing the product from the user's libraries, leaving the user to seek any recourse with the third-party they purchased from. Other legitimate storefronts, like Humble Bundle, have set a minimum price that must be spent to obtain Steam keys as to discourage mass purchases that would enter the grey market. In June 2021, Valve began limiting how frequently Steam users could change their default region to prevent them from purchasing games from outside their home region for cheaper. In 2013, Steam began to accept player reviews of games. Other users can subsequently rate these reviews as helpful, humorous, or otherwise unhelpful, which are then used to highlight the most useful reviews on the game's Steam store page. Steam also aggregates these reviews and enables users to sort products based on this feedback while browsing the store. In May 2016, Steam further broke out these aggregations between all reviews overall and those made more recently in the last 30 days, a change Valve acknowledges to how game updates, particularly those in Early Access, can alter the impression of a game to users. To prevent observed abuse of the review system by developers or other third-party agents, Valve modified the review system in September 2016 to discount review scores for a game from users that activated the product through a product key rather than directly purchased by the Steam Store, though their reviews remain visible. Alongside this, Valve announced that it would end business relations with any developer or publisher that they have found to be abusing the review system. Separately, Valve has taken actions to minimize the effects of review