Checking a Used Controller Before You Buy
Five checks that take about six minutes and catch the fault that ends most controllers.
A used controller is the purchase where visual inspection is least informative. A pad can be immaculate — no scuffs, clean grips, tight shoulder buttons — and still have worn analog sticks, because stick wear happens entirely inside a sealed mechanism and correlates with hours played rather than with how the outside looks. The cosmetically perfect controller from someone who played one game obsessively for a year is a worse buy than the scratched one from someone who played occasionally.
Drift is the specific thing to test for, and it is worth being precise about what it is. Stick drift is when an analog stick reports movement while nobody is touching it, caused in conventional potentiometer designs by physical wear on the resistive track the sensor rides against. It is the most common controller failure by a wide margin, it is progressive, and it is not repairable by cleaning once the track itself has worn.
The good news is that it takes seconds to detect with a measurement rather than a feeling. A resting reading that sits away from centre is unambiguous, and it is the difference between a working spare pad and a piece of plastic you will be annoyed about. Ask the seller to bring a USB cable, or bring one yourself — wired is faster and removes pairing from the equation.
The checklist
Tick each step as you go. All six take about a minute each, and the drift measurement near the end is the one that decides most purchases.