The I.R.S. has curtailed many audits in tax havens because obstructionist rich people can make it too time consuming to force them to pay.
In one typical case, the I.R.S. spent four years investigating a person with businesses in both the United States and an unnamed overseas tax haven. The investigation included 20 summonses, 23 demands for documents, 5 missed appointments and 2 refusals by the person being investigated to supply information. After four years, the government still did not know how much money had been moved to the tax haven.