# How to Inspect a Used Robot Before Buying: The Complete Checklist
A structured ten-minute inspection before you pay catches 90% of the problems that turn a good-value used robot into an expensive mistake. This guide gives you the exact checks to run at the point of purchase — or via video if you are buying remotely — for any robot category.
The checks are divided into three layers: universal (every robot, every category), mechanical (moving parts and wear indicators), and software (firmware, app connectivity, sensor function).
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Layer 1 — Universal checks (every robot)
These four checks apply regardless of whether you are inspecting a robot vacuum, a drone, a 3D printer, or a collaborative robot arm. Run them first, before anything category-specific.
1. The power cycle test
Turn the robot completely off — not sleep, not standby, but a full power off. Wait ten seconds. Power it back on and watch the boot sequence.
A healthy robot should:
- Complete sensor initialisation within 30 to 60 seconds
- Connect to the companion app without manual intervention
- Report ready status with no error codes
A robot that requires multiple boot attempts, takes more than 90 seconds to initialise, shows persistent error codes after a cold start, or fails to connect to the app after a fresh reset has a software or hardware problem that the seller may not have disclosed. These are typically firmware corruption, a failing storage chip, or sensor hardware failure.
2. Physical condition — body and contacts
Inspect the robot body under direct light (phone torch works well). Look at:
- Charging contacts: should be clean, bright copper or gold. Oxidised (dull, greenish) contacts cause intermittent charging. Easy to clean with a pencil eraser; worth knowing about.
- Bumper or collision sensors: press the bumper in at several points across its width. It should spring back evenly. A bumper stuck at one point indicates debris lodged in the sensor channel or internal damage.
- Optical sensors (cliff sensors, front-facing sensors): shine a torch across them in a darkened room. Any cloudiness, condensation, or smearing behind the lens surface indicates moisture ingress or cleaning product damage — a sensor board replacement rather than a surface clean.
- Structural cracks: check hinges, lid clips, dock connectors, and any panel seams for hairline cracks. A cracked housing on a pool robot or a drone is more serious than on a robot vacuum because it indicates an impact event.
3. Battery health — request documentation
Never accept "the battery is fine" without data. Ask for:
- A screenshot of the battery health from the companion app (Roborock, iRobot, Eufy, DJI Fly, Bambu Studio)
- Or a timed discharge test from 100% charge on the day of purchase
- For drones: battery cycle count from the DJI Fly app
Battery health thresholds to use as buying criteria:
- Above 85%: near-new performance, no concern
- 70 to 85%: reduced runtime, factor in replacement cost (£25–£80 depending on model) in the offer
- Below 70%: replacement required before you get reliable use — deduct the full replacement cost from the price
4. Run it — watch it do its job
Every robot must be run before you pay. There is no substitute:
- Robot vacuum: run a room clean, watch for navigation errors, check that the dock return is clean and the charging connection is made first attempt
- Pool robot: run on dry ground and listen for track bearing noise; run in water if possible
- 3D printer: print a calibration cube or benchy
- Drone: run all axes of the gimbal, check camera stabilisation, run flight mode checks on the ground before an actual flight
- Robot mower: run a 10-minute boundary wire check
A seller who refuses to run the robot before purchase is a seller to walk away from.
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Layer 2 — Mechanical checks by category
Robot vacuums
Brushes and brush housing: remove the main brush and check the brush ends for hair wrapping around the bearing points. A brush bearing choked with hair is a maintenance issue (10 minutes to clear); a worn or deformed brush is a £12 to £25 replacement. Check the side brushes for bent arms — they should spin freely with no wobble.
Dustbin and filter: remove the dustbin and inspect the filter. A filter that is grey-brown with embedded dust that does not clear by tapping is due for replacement (£8 to £15). Check the dustbin for cracks where it clips to the robot body.
Self-empty dock: if the model includes a self-empty dock, run a full empty cycle. Listen for consistent suction (not intermittent or stuttering). Check the collection bag or bin inside the dock for blockage around the inlet port.
Mop system (for combo robots): see the vacuum mop combo buying guide for detailed mop checks.
Drones
Gimbal: power on the drone and watch the gimbal initialise — it should sweep through its axes and settle to centre smoothly. Tilt the drone body manually while powered on and watch the gimbal compensate. Any jitter, axis drop, or lag indicates a ribbon cable or gimbal motor issue.
Propellers and mounts: inspect all four propeller blades for chips, cracks, or micro-cracks near the root. Even a small crack at the root is a veto — a propeller failure mid-flight is catastrophic. Check the prop mounts for any play or looseness.
Camera: record a short video clip and inspect it for banding, colour inconsistency, or focus issues. A sharp, correctly white-balanced clip from a drone recording at this light level confirms the camera sensor is sound.
3D printers
Build plate: inspect the PEI surface under a raking light for deep scratches, peeling at the edges, or warping. A warped bed is a calibration problem that can be managed but not eliminated. A damaged PEI surface is a £20 to £40 replacement.
Hotend and nozzle: check for plastic residue on the outside of the nozzle or heater block — this indicates a previous clog or heat creep event. Ask for the nozzle's replacement history. Brass nozzles last 200 to 500 hours of PLA; a nozzle at 800 hours is overdue regardless of how it looks.
Motion system: power on the printer and run a home cycle. Belts should be taut and make a consistent tone when plucked (roughly musical note A or E). A belt that sounds dead or pings at different pitches along its length has uneven tension or worn teeth.
Robot mowers
Blades and disc: remove the blade disc (requires a torx screwdriver on most Husqvarna models) and inspect each blade for scoring, deep nicks, or deformation. Replacement blades are cheap (£8 to £15 for a set of six), but severe disc wear indicates heavy use on a stone-contaminated lawn.
Boundary wire detection: place the robot inside a 30-minute boundary detection run and watch it navigate the perimeter wire. Any failure to detect the wire consistently, or navigation errors that send the robot into a boundary-crossing error repeatedly, indicates a damaged section of wire.
Rain sensor: tap the rain sensor on the top of the robot while it is running in a dry environment. It should pause and display a rain-delay message. A non-responsive rain sensor will run the mower in rain, accelerating blade rust and motor seal wear.
Pool robots
Track bearings (the critical check): as covered in the pool robot buying guide — lift the robot, run it on a dry flat surface, listen for grinding or clicking. This check is non-negotiable.
Cable and swivel: inspect the full cable length for kinking, jacket damage, or flattening. Rotate the swivel connector at the robot end — it must rotate 360° with light finger pressure.
Wall climbing: if possible, test in the pool. A robot that cleans the floor but fails to climb walls has insufficient drive torque — worn brushes or a degraded drive belt.
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Layer 3 — Software and connectivity checks
App connectivity
Open the companion app and connect to the robot. For a used purchase, the robot should be factory reset first (most sellers should do this before listing — if not, ask them to before handing over payment). After reset:
- Confirm the robot pairs to your account, not the previous owner's
- Check the app reports the correct model and firmware version
- Confirm no error codes are displayed in the app's device status screen
Firmware version
Ask for the firmware version and cross-reference it with the manufacturer's current release notes. An outdated firmware is not always a problem, but:
- More than two major versions behind suggests the robot has not been connected to the app regularly
- Some older firmware versions had battery calibration bugs (iRobot pre-22.29.x, Roborock pre-5.87) that caused premature shutdown
- Updating is free, but it tells you something about how the seller maintained the device
Map and history data
On navigation robots (Roborock, iRobot, Eufy, Husqvarna), confirm the room map has been cleared before purchase. You should not have access to the previous owner's floor plan data after buying — if you do, the robot has not been factory reset and the account is not fully transferred.
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What to do if you find a problem
A problem found before payment is leverage. A problem found after is a dispute.
If the inspection reveals a defect — battery below 70%, missing dock accessories, worn track bearings, a failing gimbal — you have three options:
- Negotiate the price down: quote the replacement cost of the defective part and ask for that amount off the asking price. Most private sellers will accept a reasonable reduction rather than relisting.
- Walk away: if the defect is more serious than disclosed and the seller is unwilling to adjust, leaving is the right call.
- Buy with eyes open: if the price already reflects the condition and you are comfortable with the repair cost, proceed.
What you should not do: pay in full for a robot with known defects and hope it works out. Every defect found before purchase is cheaper to address than every dispute after it.
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Remote inspection checklist
If buying from a distance (nationwide shipping), request a video call inspection covering:
- [ ] Full power cycle from off — watch startup
- [ ] Battery health shown in the app
- [ ] Bottom of robot (brushes removed, sensors visible)
- [ ] Any marks, scratches, or damage — close up
- [ ] Operating run (at least 5 minutes)
- [ ] Dock connection and first-attempt charging
A seller who provides all six items in a clear, unedited video is a seller you can trust. Any reluctance to show the bottom, the app, or a live run is a red flag.
Browse verified used robot listings on Robot AutoTrader — every listing on the platform has passed our physical inspection protocol before going live.