Respond to the discussion Client can establish basis in the property he is selling by providing detailed transaction documents to show his financial contributions and expenditures relating to the property. Documentation must be the original purchase record, and can include receipts or other proof of purchase. Without the necessary documentation to prove cost basis, he could either claim zero basis which results in the maximum tax -- the conservative approach -- or he could estimate the amount he paid as approximate basis -- the risky approach as he may get audited