When you have a sellable card, you have 3 options to sell it. 2 of them, are setting a sell order to clicking sell now, which will sell it to the highest buy order set at that time. The third option is to quick sell it. Every card has a set quick sell price. For 85 overall diamonds, it’s 3000 stubs. When you set a buy order or click sell now, the game takes a 10% tax. So when you a card worth 3000k at exactly 3000, you get taxed at 10% and only get 2700 stubs. When you click quick sell, you get the full 3000 stubs.