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How to check a used Samsung Galaxy before you buy it

Updated September 27, 2026

Samsung Galaxy phones are the most traded used Androids, from budget Galaxy A models to the S Ultra, Z Fold and Z Flip. Samsung ships plenty of built-in hardware tests, but there are Samsung-specific faults too: Samsung account locks, financed phones that get locked remotely, tripped Knox, green lines on AMOLED screens and worn folding hinges. This guide adds to how to check a used Android phone and focuses on what's unique to Samsung.

Tip: open soimay.com in Chrome or Samsung Internet on the Galaxy you are about to buy. There is nothing to install on the seller's phone.

1. Google and Samsung accounts

A Galaxy has two locks: the Google account lock (FRP) and the Samsung account's reactivation lock. If either is left on, the phone asks for the old account after a factory reset.

  • Settings › Accounts and backup › Manage accounts: no Google or Samsung account of the seller's may remain.
  • Settings › Security and privacy › Find My Mobile: must be off.
  • Best: have the seller remove the accounts and factory reset in front of you.

2. Financed phones that can be locked remotely

Phones bought on a payment plan through a carrier or lender can carry a remote lock (Knox Guard): if the original buyer stops paying, the phone is locked, even after a factory reset.

  • An app like "Device Services" or "Device Control" that can't be removed, or a lender's message on the lock screen: ask about it or walk away.
  • Ask where the phone was bought and whether there is a receipt. You can also ask the carrier or check the IMEI against your country's blacklist register.

3. Model code: which region

Look at Model number under Settings › About phone, for example SM-S918B/DS:

  • Ending in B (often with /DS for dual SIM): the international model.
  • U or U1: US model, usually a single physical SIM. N: Korean model. 0 (as in SM-S9180): Chinese model.

Regional models aren't bad, but you should know which one you're getting and pay accordingly: bands, warranty and features can differ. The device info test reads the model code right in the browser.

Check device specsSee the model, operating system, CPU threads, GPU, RAM and screen resolution of a phone or laptop in the browser, and compare them with what the seller claims.

Dial *#06# in the Phone app for the IMEI and compare it with Settings, the SIM tray and the box.

4. Has Knox been tripped (rooted phone)

Rooting or flashing a custom ROM trips the Knox security fuse, and it can't be undone: Samsung Wallet, Secure Folder, Samsung Health and many banking apps may stop working.

  • Open Secure Folder and try to set it up: a security error means Knox is tripped.
  • Open Samsung Wallet (Samsung Pay) and see whether it runs.
  • Restart the phone: a bootloader unlocked warning at boot means the software has been tampered with.

5. Samsung's built-in test menu

Dial *#0*# in the Phone app to open the hardware test menu: screen colours (Red, Green, Blue), Touch, speaker, vibration, Sensor and cameras. The Samsung Members › Support › Phone diagnostics app also checks each part in turn with clear results. Use both along with the soimay.com tests.

6. AMOLED screen: lines, burn-in, replacements

  • Green or pink vertical lines: a known fault on some Galaxy S and Note generations, often appearing after an update or a drop. Step through the solid colours to spot them.
  • Burn-in: fill the screen with grey and look for ghosts of the keyboard or navigation bar.
  • Non-original replacement screen: dimmer, off-colour, and the under-display fingerprint reader fails or is very slow.
Dead pixel, backlight bleed and burn-in testFind dead or stuck pixels, backlight bleed, burn-in and lines on a phone or laptop screen. Eight full-screen colours, free, no app to install.

More in how to check a used phone screen. Curved-screen models (S20+, Note 10, S22 Ultra…) often have ghost touches along the edges, so fill the grid right up to the borders:

Touch screen test: dead zones and ghost touchesSwipe to fill a grid of cells and spot dead touch zones or ghost touches on a phone or tablet. Runs full screen, free.

7. Battery and fast charging

  • Samsung Members › Phone diagnostics › Battery status: "Good" or "Weak".
  • Many phones on One UI 6.1 or later show Settings › About phone › Battery information with the cycle count.
  • Plug in an original fast charger: the lock screen should show "Super fast charging" or "Fast charging". If it doesn't, the port or battery has a problem.
Battery and charging port testSee the battery level, detect plugging and unplugging to test a loose charging port, and watch how fast the battery drains. Plus how to read battery health on iPhone, Android and laptops.

8. S Pen (Galaxy Note, S Ultra)

Pull out the S Pen: the Air Command menu should pop up. Write in Samsung Notes from edge to edge; strokes must be unbroken. Dock and undock it a few times, and on the Note 10 and later press the pen's button to take a photo remotely (this checks the pen's Bluetooth link).

9. Galaxy Z Fold and Z Flip: hinge and folding screen

Foldables are expensive, so inspect them closely:

  • The crease: a soft crease under light is normal, but cracks, bubbles or a peeling layer along the middle mean the inner screen is failing. The inner screen protector must not be peeled off by the owner.
  • Dead pixels along the fold: fill the inner screen with solid colours and watch the centre line.
  • Hinge: fold and unfold many times; it should be smooth, not gritty or loose. Half-open (Flex mode), it should hold its angle.
  • Closed, check the gap between the halves: an uneven gap can mean a bent hinge or a swollen battery.

10. Cameras, speakers, sensors, body

Open each camera (ultra-wide, main, telephoto), zoom to 3x and 10x on Ultra models, and shoot something close up to check focus. Use the camera, speaker, mic and sensor tests. Check the water indicator in the SIM slot, and look along the frame: a raised screen or a back coming away means a swollen battery.

Wrapping up

Save your results as a PDF or create a report link and QR code on the soimay.com Results page. Things to check by hand (accounts, Knox, IMEI, battery) are in the manual checklist.

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