If anything was ever wrong, or gave cause for concern, the cars were sent straight for repair. Yes, of course the fleet manager kept an eye on costs but no consideration was ever given to non-dealer servicing primarily because the guarantee would have been voided.
Most fleet cars are covered for all repairs as part of the deal anyway.
A well-serviced company car with 80k (3 years) would be a far wiser buy than a local 'shopping trolley' with 25k on the clock. I do appreciate that most would go for the lower mileage though! Few cars over three years old remain fleet owned.
You do not see many Citroen fleet cars for the reason is that they have been considered a financial liability.