Instructions
Read up on Japanese swords and swordmaking. There are several books and online resources available. Attend lectures by experts, and visit museums to build knowledge prior to buying the sword.
Find a show where Japanese swords are displayed.
Swords are often shown by members of the Japanese sword appreciation societies at shows around the U.S. (chapters of the the Japanese Sword Society of the United States), or at gun shows.
Practice the established etiquette when viewing the displayed swords (see References).
Wait until the previous person has finished watching the sword, and do not make comments about the sword until holding it. Be careful not to touch the blade with your fingers.
Decide on a sword. Ask to see the documentation, if available.
Negotiate a price, but be aware of the range which you should pay for the sword.