I'd expect no better quality of operations from the only car rental company which will accept reservations for any class of car at any time, then upon the custo

I'd expect no better quality of operations from the only car rental company which will accept reservations for any class of car at any time, then upon the customer's arrival demands that they pay to 'upgrade' to a higher class that they have in stock. Let this be another reason to avoid them. (For context, at least in the US, reputable firms will reflect their current inventory for a last-minute reservation, or attempt to project inventory for a longer-term one, and if they mess up and don't have 'your' car, they will rent you a bigger car for the rate promised.)