Most rental problems in Hanoi are the same five problems, and all five are cheaper to prevent than to settle.
Problem 1: the deposit dispute
The classic: a scratch appears at return that nobody can date. Prevention is the handover photo set - every panel, both sides, sent to the shop’s chat with a timestamp. A shop that has your photos cannot invent history; a renter who took none cannot disprove it. Do the checklist, take the photos, keep the contract until the cash is back.
Problem 2: the dead battery
Left the key on, the light switched, the bike sitting for three days? Automatics click and nothing happens. Prevention: take the key out at every stop, do not leave the ignition on with the engine off. The fix is a shop visit or a push-start (automatics cannot push-start - call the shop). Batteries are the shop’s equipment; running flat through your own neglect can become a conversation.
Problem 3: the puncture
Hanoi streets drop nails and glass, and tube-type tyres go down fast. Prevention: check pressures weekly by feel and refuel-station gauge, and avoid the litter-strewn edge of the lane. Response: ride a flat as little as possible - the tube shredding turns a cheap repair into a tyre. Inner tubes and tyres can be the renter’s responsibility depending on the situation; the puncture article explains the division.
Problem 4: the stolen bike
Bikes are stolen from sidewalks, not from guarded parking. Prevention is the lock and the parking convention: use the steering lock and a disc lock if the bike has one, and pay the few thousand dong for attended parking lots (gửi xe) rather than saving it. A stolen rental is a deposit-level conversation at best; the theft article explains where responsibility actually sits.
Problem 5: the paperwork gap
Riding without carrying a licence the police recognise, or on a bike whose registration certificate is still at the shop. Prevention: sort your licence route before renting, and take the registration certificate with the bike. Police can hold a bike whose papers cannot be produced.
The habit that prevents most of it
Treat the bike like it is yours for the period - because financially, up to the deposit amount, it is. Lock it, check it, photograph it, and when something feels wrong take it to the shop rather than hoping. The shop would rather fix a small thing at day two than a big thing at return.