Having recently been on holiday with the family, I had pre-booked car hire to allow us the freedom to see Tenerife at our own pace and when we wanted. When I booked the hire car, the booking process clearly informed me that the hire company charge for a full tank of petrol so I was to ensure I left the car empty when dropping it off after the hire. This sounded great as it would save me having to fill up before dropping the car off. But then I thought, well hang on a minute, I've just booked this hire car because the price was very reasonable compared to other companies. Now I think about it, the actual full cost is actually a lot more (50%) because no matter what, they would charge me an additional €67 to cover a tank of fuel when I dropped the car off. This left me feeling diddled - it felt a bit like a Ryan Air charge (sorry Ryan Air but unfortunately you are probably the market leaders in add ons)!
Irrational? Well perhaps yes as when you think about it, I'd have had to fill up the tank with other companies hence would have possibly spent that on petrol anyway. However, during the week I was careful to only add what I thought we'd need and despite a trip around the island on the last day, still handed it back with a quarter tank so my overall perception was the car hire was more expensive than other companies and I felt almost tricked. Despite knowing about the charge, my overall impression about the hire and hence the company is negative which is not going to make me return!
So if you have some "up-sell" opportunities in your business, take a look at them from the customers perspective to ensure you are not giving the wrong message.