Run the Once-Over on this computer.

Press Start, then press every key once. Each one lights up when the computer gets it. Keys that stay dark did not register. The Windows and Command keys are left out: the system keeps those for itself.

Start 0 of 0 keys

Use the trackpad (or the mouse that comes with it) on each pad below. A pad turns solid when it worked.

Press Show colour fields. The whole screen fills with one colour at a time: black, white, red, green, blue, grey, then a smooth fade. Click, tap or press any key for the next one. Look for dots that stay one colour, lines, dark blotches, light leaking at the edges on black, and steps in the fade. Turn the brightness up first.

Show colour fields 0 of 7 shown

Only if the screen is a touch screen: wipe a finger across every square. Squares light when the glass feels the touch (a mouse does not count). No touch screen? Mark Does not apply.

0 of 40

Unplug any headphones. Play each tone at a moderate volume. The left tone should come only from the left, the right only from the right. The sweep goes from low to high: listen for buzzing or rattling.

Play left Play right Play sweep

Press Start and allow the microphone when the browser asks. Talk normally. The bar should jump with your voice. Nothing is recorded or sent; the meter is worked out on this computer and stops when you press Stop or leave the page.

Start Peak 0

Press Start and allow the camera. You should see yourself, sharp and in colour, and the camera light (if it has one) should come on. The picture stays on this computer.

Start —

Join a network on the computer (your phone’s hotspot works), then press Test. The page asks this site for a tiny reply five times and shows the typical round trip. If Wi-Fi will not connect at all, that is a problem worth noting.

Test —

Laptops only, and only if the battery is not swollen. Unplug the charger, press Watch, then plug it back in. Chrome and Edge report when charging starts; other browsers do not, so watch the battery icon instead. Check that the charger is the right one for this model (the wattage is printed on it).

Watch —

Look and try each of these yourself. Red flags are the ones that turn the verdict into Walk away. The meet-up checklist has the same list on one printable page.

1. No bulging battery red flag laptops

   Lay it flat. The trackpad should sit level with the case, the bottom should not rock, and no seam should be pushed open. A swollen battery can leak or catch fire: if you see swelling, do not plug it in or charge it, do not press on it, and walk away (sources and what to do are in step 10).

   Result: No bulging battery

   Works Problem Not tested Does not apply

2. Case, hinges and glass

   Open and close the lid: the screen should stay where you put it. Look for cracks around the hinges, at the corners and on the glass, and for missing screws underneath.

   Result: Case, hinges and glass

   Works Problem Not tested Does not apply

3. Ports

   Bring a USB stick or your phone cable and try every USB port. If you can, plug in a monitor or TV to test the video port.

   Result: Ports

   Works Problem Not tested Does not apply

4. Locks and accounts red flag

   Restart and watch for a password box before Windows or macOS starts (a firmware or BIOS password). Windows: Settings › Accounts › Access work or school should list no work or school account. Mac: System Settings › [the seller’s name] › iCloud › Find My Mac should be off and the seller signed out of their Apple Account. If the seller cannot remove a lock, you cannot either.

   Result: Locks and accounts

   Works Problem Not tested Does not apply

5. Serial number red flag

   Compare the serial number on the sticker or the bottom case with the one in the system. Windows: Settings › System › About (or ask the seller to open the maker’s support app). Mac: Apple menu › About This Mac. They should match.

   Result: Serial number

   Works Problem Not tested Does not apply

6. System and specs

   It should start without errors. Windows: Settings › System › Activation should say active. Check processor, memory and storage in the About page against what the listing said.

   Result: System and specs

   Works Problem Not tested Does not apply

7. Storage health

   Windows: open PowerShell and run Get-PhysicalDisk | Select FriendlyName, HealthStatus; it should say Healthy. Mac: Disk Utility › First Aid should finish with no errors. Apple Diagnostics (Apple silicon: hold the power button, then press Command-D at the startup options) checks more.

   Result: Storage health

   Works Problem Not tested Does not apply