In Orzammar, there is a man in the Chamber of Assembly named Vartag. Talk to him about earning Lord Behlen's trust and he should give you papers that state that Lord Harrowmont sold the same piece of land to two people. After he gives you the papers, go to the Shaperate in the Diamond Quarter. It is at the opposite end of the entrance to the Commons. Once you are in the Shaperate, speak with the Shaperate and give him the papers. He will tell you that they are forged. After that, return to Vartag and tell him the papers are forged. After you have done this, there is a Persuade line in which you can say. Repeat as many times as desired. Note: It helps if you have a high Coercion skill or high Cunning. Also, if you made a Dwarf Commoner, your sister will take you directly to Vartag once you have entered the Diamond Quarter.