Before you buy
Checking a used monitor before you buy
A monitor either works or it does not, which is why people skip checking one. But the faults that matter are all invisible on a desktop wallpaper and all obvious on a flat colour, and they are the difference between a bargain and someone else’s problem.
The run, in order
Confirm the resolution and refresh rate the panel is actually running
Settles the specification in five seconds. A monitor sold as 144 Hz that reports 60 is either being driven by the wrong cable — fixable — or is not the model claimed.
Cycle solid colours across the whole screen
The one fault that cannot be repaired and will never improve. Clean the screen first: dust on black is indistinguishable from a stuck white pixel, and you will find far more dust.
Look at black in the darkest room you can manage
This is where most used monitors lose value, and it is the check nobody does in a bright room. Judge it at the brightness you would actually use, not at maximum.
Count the near-black and near-white steps you can separate
Catches a panel whose settings have been pushed hard, and a signal range mismatch. Both look like a bad panel and are usually free to fix, so it is worth knowing which you have before you value it.
Look for tinting and uniformity on solid fields
A cast across the whole screen is a setting. A cast in one region is the panel, cannot be adjusted away, and is a real reason to pay less.
Watch a moving pattern at speed
Reveals a panel with failing overdrive, and tells you whether the response actually justifies the refresh rate on the box.
Try every input, with your own cable
Not a browser test. Inputs fail individually and a seller who only ever used one port genuinely may not know. Bring the cable you intend to use, because a monitor that works over HDMI and not DisplayPort is worth less to you specifically.
Press gently on the bezel corners and watch for changes
A picture that flickers or shifts under light pressure means a loose internal connection, which is a repair rather than a discount.
Bring these three things
A laptop, the cable you intend to use, and a microfibre cloth. The cloth is not a joke: most reported dead pixels on a used monitor are dust, and finding that out after you have paid is worse than finding it out before.
The order, and why
Resolution first, because it settles what the monitor is before you spend time on how good it is. Then the panel faults that cannot be repaired, then the ones that are only settings, then the physical checks. If something in the first three steps ends the deal, you have spent two minutes.
What each finding is worth
| What you find | What it means for the price |
|---|---|
| Dead pixel, centre of screen | Walk away |
| Dead pixel, far corner | Significant discount if you can live with it |
| Picture changes when you press the frame | Walk away |
| Heavy backlight bleed | Substantial discount |
| Regional colour cast | Substantial discount, cannot be fixed |
| Crushed blacks or clipped whites | Usually free to fix — check settings before valuing it |
| Ghosting at speed | Discount on a monitor sold for gaming, otherwise minor |
| One dead input | Discount, unless it is the one you need |
The mistake almost everyone makes
Testing in a bright room. Bleed, black uniformity and low-level detail are all invisible under normal lighting, which is exactly why a seller can honestly believe a monitor is flawless. If you cannot darken the room, at least cup your hands around the edges of the screen while the black test runs — it is enough to see the difference.
Common questions
What is worth walking away from?
A dead pixel in the middle of the screen, and any picture that changes when you press the frame. The first cannot be fixed and you will see it every day; the second is an internal fault that will get worse. Bleed, tint and a tired overdrive setting are all things to pay less for rather than reasons to leave.
The seller has no computer to plug it into.
Then you cannot check it, and no amount of looking at a powered-off screen substitutes. Bring a laptop. Every test here runs in a browser, so a laptop and a cable are the entire kit.
How much bleed is too much?
The practical test is whether you can see it in normal room lighting on ordinary content — not on a black screen in the dark, where every monitor ever made shows some. If it is visible during a film with a lamp on, it is too much.
Does burn-in apply here?
On an LCD, no — what looks like burn-in is usually temporary image retention that clears. On an OLED it is permanent and worth checking specifically: a solid grey field will show it as faint outlines of whatever was left on screen for months.
Is a monitor with a stuck pixel worth trying to fix?
It costs ten minutes to try, and it works on stuck pixels rather than dead ones. Do the fixing after you have used the fault to negotiate, not before.