Start with the seller's specification
Compare the advertised model and hardware with what the operating system reports. A model name alone may cover several CPU, display and storage configurations.
Inspect the outside first
Look at the hinges, corners, underside, screws, charging connector and display bezel. Signs of impact, missing screws or a lifted trackpad can indicate previous repair or battery swelling.
Test the screen
Use the dead pixel test, vary brightness and move the lid slowly to check for flicker. A browser can help display test colors, but you must inspect the panel visually.
Test every input
Use the keyboard test and mouse/trackpad test. Pay extra attention to modifier keys, arrows, function keys and click/scroll gestures.
Check camera and audio
Run the webcam, microphone and speaker tests. These require browser permission or user interaction.
Use system diagnostics for the rest
Battery wear, SSD health, temperatures, firmware passwords and hardware errors need operating-system or manufacturer tools. Do not rely on a browser-only score for those checks.
Continue with the guided checkup
Use the guided used laptop checkup to organize the browser-based tests into a simple report.