Indicating in a Bill of Sale that the item is 'sold as seen' ensures that the seller is not liable for any flaws or damages related to the product. In other words, if a Bill of Sale expressly states that the goods are 'sold as seen', there can be no argument over the condition of the property in the future. This protects the seller from any liability after purchase that arises because, for example, the item does not work properly.
For more information, read Bills of sale.