How to: Find a used Sub-Zero that will last.
Step one: Identify your units model information.
The first thing to do when buying used is to identify your model information. Your model tag will have important information on it such as the production date, the model number and serial number. I think the most important thing here is production date, lets try to stay away from 20+ Year old units unless you are looking specifically for an older unit for aesthetic purposes.
Step Two: Evaluate the units structural condition
The most important factor in whether or not we think a unit is repairable for the long term is the condition of the frame and doors. Check out this link on whether or not your unit should be repaired. This is also a great way to evaluate a used unit. Just like a car, evaluate around and even under the machine for rust and wear and tear.
Newer units will be made of plastic, you can tell whether or not it has been maintained by looking at the frame of the unit. On units that have not been maintained they may be starting to "yellow" along the door frame from heat exhaustion. This would mean that the unit has been running hot due to lack of maintenance or an unresolved issue such as a bad fan motor causing the machine to run hot for long periods. If we see a "yellow" frame we know the machine has lived a rough life cycle. You may also see stress fractures and cracks on the plastic around the door, this could be from overheating, poor installation or even an accident that cracked the frame.
Step Three: Check for error codes and your temperature logs.
Watch this video on how to run through your temperature logs and get an idea of whats happening on an hour to hour basis with the machine.
Step Four: Evaluate Installation Find and installer.
Arguably the most important factor, was the machine installed correctly? Is there floor going up to the machine or all the way under it? Has it been sitting straight all these years or is it sinking into the ground and crooked? You probably won't be moving the unit yourself, do you have a de-installer and reinstaller? Can they get it out to their vehicle without damaging it and are they familiar on how to move a sub-zero ?