On the contrary, when renting a car a couple of years ago I had following situation - I booked a car and paid, then I arrived at the airport, and at the counter I was told:
* 5EUR/day more because I'm below 25yo
* 5EUR/day more because it's a diesel car ("so I don't want diesel" - "but we have only diesel")
* gas policy is full/empty, so I have to pay for gas in advance; I check the contract and it says I have to pay "market rate", I check online and market rate is 20% less than what they want me to pay, I say this is not market rate, they say it includes surcharge for fueling the car.
In the end I didn't have much choice and rented the car, but the experience was much worse than buying air tickets.
On the plus side, most rental cars don't charge for canceling or missing a reservation, returning early, or just not showing up--so there's that.
As an American living in Europe, I found that some US insurers will issue a 'driver only' policy that covers you while driving rentals in the USA on your European license. I'm paying $24/year for mine which has generous limits and is much cheaper than the coverage rental agencies offer.
Also slightly unrelated but don't dare call British Airways to enquire about changing your flight or you will not be able to check in online and you will get the worst seats when you show up for your flight. This is true even if you make no changes, your booking is put in to some kind of frozen state and the phone agents are unable to reverse this. You must visit the BA desk at an airport in person to have this corrected. Bizarre, but this was confirmed by multiple people at BA who I spoke to after having it happen to me.
As for gas policy whenever I rented a car it was full/full.
- Bed sheets
- key deposits
- shower access
- locker usage