First, the build era. Knowing a neighborhood runs older - Altadena, San Marino, South Pasadena, and the inner communities closer to the 2-to-5-mile ring tend to skew earlier - tells a tech what kind of spring mount and track hardware to expect before he even opens the truck.
Second, the seals and rollers. In a mild temperate climate, these fail from sun and age rather than cold, so a tech checks for cracking, brittleness, and UV wear rather than ice damage or frozen tracks.
Third, cycle count on the spring, not just its age. A door on a house built in 1959 that's been opened twice a day for decades has seen more cycles than a much older door used rarely.
Fourth, whether the opener has been replaced separately from the door - common in this area, since owners often upgrade the motor before touching the door itself.
Fifth, and this is the one we're honest about: if the hardware is original and a matching part isn't available, we say so and talk replacement instead of pretending a patch will hold.