What should I check before buying a used phone?

Battery health (the single biggest depreciator), screen for dead pixels, every camera, all speakers, all microphones, every button, charging port responsiveness, network radios. This wizard automates the digital subset; the manual list covers the rest.

How can I tell if a used phone has been water-damaged?

On iPhones, look at the SIM-tray indicator (red = water-detected). On Androids, check the inside of the SIM tray and headphone jack with a torch — many have similar dots. Internally, water damage shows up as failing speakers or microphones, sluggish touch, or corrosion-pattern audio dropouts.

What's a fair price discount for a used phone?

Compared to a new equivalent: ~25% off for under 12 months, ~40% for 12-24 months, ~50%+ for 24+ months. Battery wear, screen condition, and any failed test from this wizard are all negotiation leverage.

Wizard / W10

Used phone check.

12-step certified pre-owned diagnostic. Run this in the seller's hand. Auto-tests in 90 seconds, plus a manual visual checklist. Generate the Buyer's Report at the end.

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Manual follow-ups browser cannot measure

iOS Battery Health (iPhone only)

Settings → Battery → Battery Health. Under 80% maximum capacity = throttling kicked in, negotiate or budget for the £89 replacement. Cycle count below 500 on a 2-year-old phone is excellent.
Camera test (front + back)

Open the camera app. Take a photo with each lens (wide, ultrawide, tele if present). Check for dust spots, focus issues, colour casts. Black blobs in the frame = sensor damage.
Speaker + earpiece test

Open /audio/stereo (after the wizard). Both bottom and top speakers should be equal loudness. Make a real call — earpiece speaker is rarely tested in resale.
Microphone test (top + bottom)

/microphone/waveform — record yourself talking close to each mic, play back. Crackle = water damage.
Buttons + ports

Volume up/down, power, mute switch (iPhone) or action button. Lightning / USB-C: plug in a charger, confirm fast-charging icon appears. Wireless pad if applicable.
Screen dead-pixel sweep

/monitor/dead-pixel — every solid colour. Look for stuck pixels, dust under glass, burn-in (especially status bar / nav bar areas on OLED).
Touch sweep

/touch/multitouch — drag a fingertip across every region. Dead patches = digitiser damage.
IMEI / blacklist check

Settings → General → About (iOS) or *#06# (Android). Cross-check the IMEI on icloud.com/find (iOS) or a service like checkmend.com for blacklist status. Stolen phones cannot be activated.

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