There is something called backup withholdings for non-residents when a non resident sells a piece of property. The attorney/CPA or real estate agent must withhold 30% of the proceeds and submit them to the US Treasury. Then the non-resident alien must file a tax return as a non-resident reporting the sales transaction and caim a refund of the amount withholing, if necessary. The reason for this withholding is that if the withholding is not done, then there is no way to obligation the non-resident to file a tax return and pay taxes on the transfer of property. This way, the US government doesnt have to chase the non-resident seller for tax money.