Responsibility for actions with the account after purchase lies with the buyer. The buyer took some action that led to the account being blocked. After purchasing an account, the buyer is the owner of the account. He was provided with all the data for this. First activation key. Screenshot of key purchase receipt. First data (email with letters about registering an account and purchasing the first game, pwd). The buyer could transfer the account to a third party after the purchase. Or change data to previously blocked data on Steam. Do anything that could lead to such a blockage. Prior to the purchases and actions of the buyer regarding the account, the account had not had any blocking for more than 2 years. The screenshots that the buyer sends do not prove that his data was not linked or used to other blocked Steam accounts. Or that he did not transfer the account to a third party.