Generally speaking, if the buyer needs to pay the difference after the auction, it should clearly state this requirement in the auction announcement. In this way, people who participate in the auction will know in advance and make corresponding preparations.
If the court or relevant institutions do not clearly stipulate the policy of making up the difference in the announcement, and then ask the buyer to make up the difference, some judicial interpretations believe that the judgment should be made according to the principle of reasonable expectation. In other words, if it is reasonable and foreseeable to make up the difference, the judge may decide that the buyer is obliged to make up the difference.
However, the specific judgment depends on relevant laws and judicial practice. It is suggested that you consult professionals, such as lawyers or legal advisers, according to the actual situation to obtain accurate legal advice.