• Know who you are buying from. Frauds abound. A reputable dealer should be able to provide guarantees of authenticity and warranties on work — and should be able to buy your timepiece back from you down the road.

• John Reardon, head of watches at Christie’s, says: “In real estate it’s location, location, location. With watch investing, it’s condition, condition, condition.” The less polishing from restoring and the more original parts that remain, the more valuable a timepiece.

• Keep the original box and papers. Original certificates are similar to a birth certificate, verifying its origins and authenticity, and can add value at resale.

• Look for rarity and originality. Pieces made in limited editions tend to draw the highest prices, especially at auction. At the same time, timepieces with complications like moon phases, tourbillons, and perpetual calendars have remained desirable over centuries.

This story is from the June 16, 2014 issue of Fortune.