Try some basic psychology. Put yourself into the shoes of that person. Most IRS employees are 9-to-5 types just trying to do a job and get through the day. Their pay is often too low to support a family, particularly in areas with a high cost of living. They deal with hostile and untruthful citizens all day long. Understandably, IRS morale is low.
If an agent doesn't seem to like you for some reason, instead of escalating the war, try to clear the air and relieve the tension. For instance, say, "I'm sorry we can't get along. But let's try to get through this and get it over with, okay?"
If conciliation fails, speak to the agent's manager, whose job is to close cases and smooth things over with taxpayers.
While dishonest employees are a rarity at the IRS, if an IRS employee lies or suggests you give him or her any favors, report the person to the IRS by calling 800-829-1040 or contact the Taxpayer Advocate Service at 877-777-4778. You can also write the IRS at 1111 Constitution Ave., NW Washington, D.C. 20224. You can make your complaint anonymously or sign your name. Either way, don't expect to hear the results of the investigation.
For tips on dealing with a difficult auditor and other audit problems, see Stand Up to the IRS, by attorney Frederick Daily (Nolo).