A used e-bike can save you a lot, but it carries a risk a normal used bike does not: the battery. A worn or abused battery is expensive to replace and can be unsafe, so most of your checking effort goes there. Work through this before you buy.
The battery is the whole game
- Ask the age and rough charge cycles. Batteries fade with age and use; a pack more than 3 to 4 years old, or heavily used, may be near replacement
- Check for any swelling, damage, corrosion on the contacts, or a case that has been opened. Walk away from a damaged pack
- Turn it on and check the charge holds and the range display looks sane. If you can, ride it far enough to see the charge drop at a believable rate
- Find out what a replacement battery costs for that model. On some bikes it is most of the value of the bike
Motor, frame and running gear
Ride it. The motor should engage smoothly with no grinding, rattles or cutouts. Check the frame for cracks, especially around welds and the motor mount, and check the wheels are true. Brakes, tyres, chain and cassette are normal wear items, but factor replacements into your offer.
Legal and ownership checks
Confirm the bike is a road-legal 250W pedal-assist model if you plan to ride on roads and paths, not a derestricted or high-power machine you cannot legally use. Ask for the original purchase receipt, both to prove it is not stolen and to see if any warranty transfers. Be wary of a deal that is too cheap with no history.