"Come/Go under the hammer" is a colloquial expression which refers to an object being put up for auction. There are several synonymous phrases that can be used to convey the same meaning more appropriately in different contexts. For instance, "up for sale" is a more formal term that is commonly used in advertising. "On the block" is a more casual way of expressing that the item is up for sale. "On the auction block" is used to describe the item that is up for auction. Additionally, "under the gavel" or "going once, going twice, sold" are also commonly used phrases to convey that the item is being auctioned off.