I have one Ford Ka (52reg) courtesy car & a Landrover Discovery (P reg V8)for my own use,which i also use as a courtesy car when needed,(which is most of the time).I charge them both out at £10 /day & get the customers to sign a form to say that they will refill with fuel that they have used,pay the first £500 damage,pay any speeding fines etc.
Quite often the cars are returned empty or i am told "i only went to so & so & didn't see any petrol station.The Ford Ka was an ex demonstrator when we got it in as new condition.Within the first 3 or 4 uses there was quite a bit of damage & one time it was returned so low on fuel,that my wife ran out driving to the petrol station approx 3 miles away.
Sorry for such a long post,but i think that if you are going to provide a courtesy car, you need to charge to cover damage etc & to be able to replace it.Most customers appreciate the use of the car & realise that hiring a car for the day is a lot more hastle & costs more & also usually it is more convenient than having to get a lift etc.I also find that the customers that complain about the cost are a pain in the ass anyway & i usually don't want them to come back.
Kind regards, Andrew