Microtransactions in Crab Game are summarized as...
The game is free-to-play, but does feature optional cosmetic purchases. Most of these are through the Steam Community Market, meaning their value is determined entirely by the players.
The game features Lootboxes which are earned for free. These have a random chance to be earned at the end of a game. With a maximum amount of Lootboxes you can earn each day. For now these boxes can not be purchased, but that may change in the future. You do not need to purchase a key to open these boxes. The cosmetics you can get from Lootboxes vary in rarity. Some are very common, while others are very rare. Furthermore these items can have random colors or a "shiny" status, making them more rare. All cosmetics can be sold on the Steam Community Market, with the more rare cosmetics going for ridiculous prices.
The game also features a shop with items that can be purchased directly, without a need for lootboxes. As of right now this shop contains only a few items, all of which are fairly cheap.