You are selling a slot on a calendar, not an item from a shelf
A rental business does not sell vehicles; it sells the right to use one between two dates. That makes availability the core record: a unit committed for a period, with the period itself being the scarce resource. Odoo's rental capability models that directly, so a booking reserves the calendar rather than decrementing a stock count that was never the real constraint.
Condition and deposits are where disputes start
Handover and return are the moments that decide whether a rental was profitable. Recording condition at both ends against the specific unit, with the deposit held and released against that record, turns a later disagreement into a documented sequence rather than a recollection.
Fines, tolls and mileage arrive after the customer has gone
Traffic fines and toll charges typically surface days or weeks after return, and by then the contract is closed and the customer has left. They need to attach to the original contract and the specific unit so they can be recharged with evidence, which is difficult once the rental has been archived as complete.